/* Astray design system.
 *
 * Token names follow shadcn/ui conventions (--background, --card, --primary,
 * --muted-foreground, --border, --ring, --radius) so the vocabulary is one a
 * reader already knows, and every component below is composed from that set
 * rather than from ad-hoc values. The visual language is the one Aceternity
 * popularised: an aurora wash behind glass panels, a cursor-tracked spotlight,
 * a conic border beam on the single most important surface, a shimmer that
 * crosses the primary action. It is hand-written CSS because this project has
 * no build step, and adding React, Tailwind and Framer Motion to a working
 * vanilla frontend would mean rebuilding the verified grounding client to
 * arrive at the same pixels.
 *
 * Colour is measured, not eyeballed. Every text-on-background pair here was run
 * through APCA (0.98G-4g) and holds Lc >= 75 for body copy and Lc >= 60 for
 * large or secondary text, including the worst case of a translucent card
 * composited over the brightest point of the aurora. Two hues carry meaning and
 * nothing else does: coral is the student's error, green is a machine-verified
 * fact. The violet and teal in the aurora are decorative and never appear on a
 * control, a state, or a value.
 *
 * Motion follows one rule. Expressive where it is rare (a view entrance, the
 * diagnosis landing), nearly invisible where it repeats (hover, focus, typing).
 * Every animated state change also has a static cue, so the whole system can be
 * switched off by prefers-reduced-motion without losing information.
 */

/* ------------------------------------------------------------------- tokens */
:root {
  color-scheme: dark;

  /* Surfaces. Cards are translucent so the aurora reads through them, at an
   * alpha high enough that the composite never moves measured text contrast by
   * more than ~2 Lc away from the opaque value. */
  --background:   oklch(0.148 0.008 274);
  --background-2: oklch(0.183 0.009 274);
  --card:         oklch(0.216 0.009 274 / 0.86);
  --card-solid:   oklch(0.216 0.009 274);
  --muted:        oklch(0.262 0.009 274);
  --muted-hover:  oklch(0.300 0.010 274);
  --popover:      oklch(0.232 0.010 274);

  /* Text. Measured on --card: 0.967 -> Lc 92, 0.856 -> Lc 76, 0.775 -> Lc 64.
   * --muted-foreground never carries body copy. */
  --foreground:       oklch(0.967 0.003 274);
  --foreground-2:     oklch(0.856 0.008 274);
  --muted-foreground: oklch(0.775 0.011 274);

  /* Lines. Pure white alpha, never a tinted neutral: a tinted hairline picks up
   * the surface beneath it and reads as grime along the edge.
   *
   * --input is dramatically lighter than --border, and measurement is why. The
   * card is already close to black, so darkening it to make a field well barely
   * moves luminance at all: the 24%-black fill measures 1.05:1 against the card,
   * which is invisible. The border is therefore the only thing saying "you can
   * type here", not a reinforcement of the fill, so it has to carry the whole
   * cue on its own. 0.60 clears both WCAG 1.4.11's 3:1 (it reaches 7.0:1) and
   * APCA Lc 45 against the card, the field fill, and the bare background, so an
   * input placed outside a card later is still compliant. */
  --border:        oklch(1 0 0 / 0.08);
  --border-strong: oklch(1 0 0 / 0.15);
  --input:         oklch(1 0 0 / 0.60);
  --input-hover:   oklch(1 0 0 / 0.72);
  --ring:          oklch(0.862 0.058 250);

  /* Brand coral, taken from the mark. L sits at 0.780 because a saturated warm
   * hue has very little contrast headroom: this is where a near-black label on
   * the filled button finally clears APCA 60 (it reaches 62.7, and no lightness
   * of this hue reaches 75). Chroma is capped at the sRGB gamut boundary for
   * that lightness. --primary is therefore never a body-text colour. */
  --primary:            oklch(0.780 0.129 29.2);
  --primary-hover:      oklch(0.830 0.095 29.2);
  --primary-foreground: oklch(0.140 0.045 29.2);
  --primary-soft:       oklch(0.780 0.129 29.2 / 0.13);
  --primary-soft-2:     oklch(0.780 0.129 29.2 / 0.20);
  --primary-line:       oklch(0.780 0.129 29.2 / 0.42);
  --primary-glow:       oklch(0.780 0.129 29.2 / 0.28);

  /* Only ever means "SymPy ran and agreed". */
  --success:      oklch(0.812 0.152 152);
  --success-soft: oklch(0.812 0.152 152 / 0.12);
  --success-line: oklch(0.812 0.152 152 / 0.32);

  /* Decorative only. */
  --aurora-a: oklch(0.68 0.20 28);
  --aurora-b: oklch(0.60 0.20 288);
  --aurora-c: oklch(0.66 0.14 208);

  /* Radii. Nested surfaces are concentric: outer = inner + padding. */
  --radius-xs:   6px;
  --radius-sm:   9px;
  --radius:      13px;
  --radius-lg:   20px;
  --radius-xl:   26px;
  --radius-full: 999px;

  /* Elevation is a ring plus depth rather than a border, so one token works
   * over the card, the aurora and the video without being redesigned per
   * background. Structural lines stay real borders. */
  --ring-1:      0 0 0 1px oklch(1 0 0 / 0.08);
  --shadow-sm:   var(--ring-1), 0 1px 2px oklch(0 0 0 / 0.30);
  --shadow-card: var(--ring-1), 0 1px 2px oklch(0 0 0 / 0.24),
                 0 16px 40px -24px oklch(0 0 0 / 0.60);
  --shadow-pop:  var(--ring-1), 0 12px 36px -12px oklch(0 0 0 / 0.70);
  --shadow-glow: 0 0 0 1px var(--primary-line), 0 8px 30px -10px var(--primary-glow);

  --sans: ui-sans-serif, system-ui, -apple-system, "SF Pro Text", "Segoe UI", Roboto, sans-serif;
  --mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;

  --ease: cubic-bezier(0.2, 0, 0, 1);
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
}

@property --beam {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  min-height: 100dvh;
  background: var(--background);
  color: var(--foreground);
  font-family: var(--sans);
  font-size: 15px;
  line-height: 1.55;
  letter-spacing: -0.006em;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

button { font: inherit; cursor: pointer; }

::selection { background: var(--primary-soft-2); color: var(--foreground); }

:focus-visible {
  outline: 2px solid var(--ring);
  outline-offset: 2px;
}

/* ----------------------------------------------------------------- backdrop */
/* Two fixed decorative layers beneath everything. The aurora is three blurred
 * radial washes drifting on a long loop; the grid is a 1px lattice masked to
 * dissolve before it reaches any edge, so it never ends in a visible seam.
 * Neither is interactive and both are hidden from assistive tech. */
.backdrop {
  position: fixed;
  inset: 0;
  z-index: -1;
  overflow: hidden;
  pointer-events: none;
}

.backdrop::after {
  content: "";
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(to right, oklch(1 0 0 / 0.032) 1px, transparent 1px),
    linear-gradient(to bottom, oklch(1 0 0 / 0.032) 1px, transparent 1px);
  background-size: 46px 46px;
  mask-image: radial-gradient(ellipse 80% 58% at 50% 0%, #000 18%, transparent 76%);
  -webkit-mask-image: radial-gradient(ellipse 80% 58% at 50% 0%, #000 18%, transparent 76%);
}

/* The washes are already soft (each gradient is fully transparent by 66%), so
 * the blur only has to smooth the banding. A large radius here is the most
 * expensive thing on the page and this is a screen that plays video, so it is
 * kept to the smallest value that still looks continuous. */
.aurora {
  position: absolute;
  inset: -28% -20% auto -20%;
  height: 128%;
  filter: blur(46px);
  opacity: 0.4;
}

/* Transform only, so the drift stays on the compositor and never triggers
 * layout or paint. */
.aurora span {
  position: absolute;
  display: block;
  border-radius: 50%;
  animation: drift 30s var(--ease) infinite alternate;
}

.aurora span:nth-child(1) {
  inset: 2% auto auto 5%;
  width: 46vw;
  height: 42vw;
  background: radial-gradient(circle, var(--aurora-a), transparent 66%);
}

.aurora span:nth-child(2) {
  inset: -8% 2% auto auto;
  width: 40vw;
  height: 40vw;
  background: radial-gradient(circle, var(--aurora-b), transparent 66%);
  animation-duration: 38s;
  animation-delay: -12s;
}

/* Kept below the headline band on purpose. Sitting this one directly behind the
 * display type lifted the background right where the second line falls, which
 * cost the headline visible contrast even though the text colour never changed.
 * It now washes the cards instead, where the surfaces are opaque enough to stop
 * it reaching the text. */
.aurora span:nth-child(3) {
  inset: 56% auto auto 30%;
  width: 34vw;
  height: 26vw;
  background: radial-gradient(circle, var(--aurora-c), transparent 68%);
  animation-duration: 34s;
  animation-delay: -22s;
}

@keyframes drift {
  from { transform: translate3d(0, 0, 0) scale(1); }
  to   { transform: translate3d(6%, 4%, 0) scale(1.16); }
}

/* ------------------------------------------------------------------- topbar */
.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 28px;
  padding: 13px clamp(18px, 4vw, 44px);
  background: oklch(0.148 0.008 274 / 0.72);
  backdrop-filter: blur(16px) saturate(1.6);
  -webkit-backdrop-filter: blur(16px) saturate(1.6);
  border-bottom: 1px solid var(--border);
}

.brand { display: flex; align-items: center; border-radius: var(--radius-sm); outline-offset: 4px; }
.brand img { display: block; height: 26px; width: auto; }

.nav {
  display: flex;
  gap: 3px;
  margin-inline-start: auto;
  padding: 3px;
  background: oklch(1 0 0 / 0.04);
  border-radius: var(--radius);
  box-shadow: inset 0 0 0 1px var(--border);
}

/* Concentric: a 13px shell with 3px padding gives a 10px inner radius. */
.nav a {
  padding: 6px 14px;
  border-radius: 10px;
  color: var(--muted-foreground);
  font-size: 13.5px;
  font-weight: 550;
  text-decoration: none;
  transition-property: color, background-color;
  transition-duration: 140ms;
  transition-timing-function: ease-out;
}

.nav a:hover { color: var(--foreground); background: oklch(1 0 0 / 0.05); }
.nav a.is-active { color: var(--foreground); background: var(--muted); box-shadow: var(--shadow-sm); }

/* ------------------------------------------------------------------- layout */
main { display: block; }
main:focus { outline: none; }

.pane {
  width: 100%;
  max-width: 1360px;
  margin: 0 auto;
  padding: clamp(28px, 5vw, 56px) clamp(18px, 4vw, 44px) 96px;
}

.pane-narrow { max-width: 760px; }

/* Section rhythm. The gap between groups is more than double the gap inside
 * one, so grouping is carried by space rather than by rules. */
.pane > * + * { margin-top: 26px; }
.pane > .hero + * { margin-top: 40px; }

/* --------------------------------------------------------------------- hero */
.hero { padding-block: clamp(6px, 3vw, 24px) 4px; }

.eyebrow {
  display: flex;
  align-items: center;
  gap: 7px;
  margin: 0 0 14px;
  color: var(--primary);
  font-size: 13px;
  font-weight: 600;
  /* Sentence case, and no tracking beyond the face's own. Wide tracking is a
   * fix for a problem all-caps creates -- caps are uniform-height blocks that
   * jam together -- so carrying it over to sentence case just pulls the word
   * apart. The size goes up 1px because lowercase reads smaller than caps at
   * the same point size. */
  letter-spacing: 0;
}

/* The sprite is a definitions-only <svg>: it must be in the document for <use>
 * to resolve, and must never occupy a line box. */
.sprite { position: absolute; width: 0; height: 0; overflow: hidden; }

/* Sized a little larger than the artwork it replaces. The small-size cut has
 * four strokes instead of eight, so it can afford the room, and it needs it:
 * the arms are ~23 of 248 units thick, which is only just over a pixel once
 * this is 14px tall. */
.eyebrow-mark { display: block; flex: 0 0 auto; width: 15px; height: 15px; }

.display {
  margin: 0;
  max-width: 23ch;
  font-size: clamp(34px, 5.4vw, 52px);
  font-weight: 640;
  line-height: 1.06;
  letter-spacing: -0.032em;
  text-wrap: balance;
  /* Near-white at the top falling slightly at the bottom reads as light across
   * the type. The falloff is deliberately shallow: at a deeper bottom stop a
   * two-line headline reads as though its second line were de-emphasised
   * rather than lit, and the stop stays well above the body-text floor. */
  background: linear-gradient(180deg, var(--foreground) 46%, oklch(0.905 0.006 274));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

/* Without clip-to-text support, `color: transparent` would erase the headline
 * rather than degrade it. */
@supports not ((background-clip: text) or (-webkit-background-clip: text)) {
  .display { background: none; color: var(--foreground); }
}

.lede {
  margin: 18px 0 0;
  max-width: 58ch;
  color: var(--foreground-2);
  font-size: 16.5px;
  line-height: 1.62;
  text-wrap: pretty;
}

/* -------------------------------------------------------------------- cards */
.card {
  position: relative;
  padding: clamp(20px, 2.6vw, 28px);
  background: var(--card);
  backdrop-filter: blur(14px) saturate(1.3);
  -webkit-backdrop-filter: blur(14px) saturate(1.3);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
}

.card-title {
  margin: 0;
  font-size: 15.5px;
  font-weight: 600;
  letter-spacing: -0.012em;
}

.card-head { margin-bottom: 18px; }
.card-head .card-title + .field-hint { margin-top: 5px; }

/* Cursor spotlight. --mx/--my are written by app.js on pointermove; the layer
 * is a soft radial that follows the pointer and fades in on hover. Opacity is
 * the only animated property, at 200ms, so a high-frequency hover costs almost
 * nothing. Without a pointer the vars never set and nothing appears. */
.card-lit::before {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: radial-gradient(
    460px circle at var(--mx, 50%) var(--my, 0%),
    var(--primary-soft-2),
    transparent 68%
  );
  /* Behind the content, not over it. A positioned pseudo-element paints above
   * the card's non-positioned in-flow content, so this layer used to sit on top
   * of the inputs and the textarea: `screen` spared the near-white text, which
   * is already at the ceiling, but the fields' own surface is a translucent
   * dark (`oklch(0 0 0 / 0.24)`) and screen can only lighten, so the glow
   * washed coral straight across every box it passed under.
   *
   * A negative z-index paints in the step between the element's own background
   * and its in-flow content, which is exactly the band this belongs in: above
   * the card surface it is meant to light, below every field and every line of
   * type. It stays inside the card because the card's backdrop-filter makes it
   * a stacking context, so -1 cannot escape to sit behind the page. */
  z-index: -1;
  /* Kept, and now unambiguous: the only thing left beneath this layer is the
   * card surface, so `screen` lightens that and nothing else. */
  mix-blend-mode: screen;
  opacity: 0;
  transition: opacity 200ms ease-out;
  pointer-events: none;
}

.card-lit:hover::before { opacity: 1; }

/* Border beam: a conic sweep clipped to a 1px ring by masking the content box
 * out of the padding box. Applied to exactly one surface in the product, the
 * diagnosis, which is the entire reason the page exists. */
.card-beam::after {
  content: "";
  position: absolute;
  inset: 0;
  padding: 1px;
  border-radius: inherit;
  background: conic-gradient(
    from var(--beam),
    transparent 0deg 62deg,
    var(--primary-line) 84deg,
    var(--primary) 92deg,
    var(--primary-line) 100deg,
    transparent 122deg 360deg
  );
  mask: linear-gradient(#000 0 0) content-box, linear-gradient(#000 0 0);
  -webkit-mask: linear-gradient(#000 0 0) content-box, linear-gradient(#000 0 0);
  mask-composite: exclude;
  -webkit-mask-composite: xor;
  animation: beam 5.5s linear infinite;
  pointer-events: none;
}

@keyframes beam { to { --beam: 360deg; } }

/* ----------------------------------------------------------------- controls */
.btn {
  --btn-bg: var(--muted);
  --btn-fg: var(--foreground);
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 18px;
  min-height: 42px;
  overflow: hidden;
  background: var(--btn-bg);
  color: var(--btn-fg);
  border: 0;
  border-radius: var(--radius);
  font-size: 14.5px;
  font-weight: 570;
  letter-spacing: -0.008em;
  box-shadow: var(--shadow-sm);
  transition-property: background-color, box-shadow, scale, color;
  transition-duration: 150ms;
  transition-timing-function: ease-out;
}

.btn:hover:not(:disabled) { --btn-bg: var(--muted-hover); }
.btn:active:not(:disabled) { scale: 0.96; }
.btn:disabled { opacity: 0.5; cursor: not-allowed; box-shadow: var(--ring-1); }

.btn-primary {
  --btn-bg: var(--primary);
  --btn-fg: var(--primary-foreground);
  font-weight: 600;
  box-shadow: var(--shadow-glow);
}

.btn-primary:hover:not(:disabled) {
  --btn-bg: var(--primary-hover);
  box-shadow: 0 0 0 1px var(--primary), 0 10px 34px -8px var(--primary-glow);
}

/* Shimmer: a highlight band crossing the fill once per hover. Transform only,
 * and it never loops, so it reads as a response to the pointer rather than an
 * animation competing for attention. */
.btn-primary::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(100deg, transparent 42%, oklch(1 0 0 / 0.34) 50%, transparent 58%);
  transform: translateX(-110%);
  pointer-events: none;
}

.btn-primary:hover:not(:disabled)::after {
  transform: translateX(110%);
  transition: transform 680ms ease-out;
}

.btn-quiet {
  --btn-bg: transparent;
  --btn-fg: var(--foreground-2);
  box-shadow: inset 0 0 0 1px var(--input);
  text-decoration: none;
}

.btn-quiet:hover:not(:disabled) { --btn-bg: oklch(1 0 0 / 0.05); --btn-fg: var(--foreground); }

.btn-send { flex: 0 0 auto; width: 42px; padding: 0; }

/* The microphone, in four states.
 *
 * This is the whole reason the styling is worth this much room. The microphone
 * can now be open without anyone having pressed anything, and a student who
 * cannot tell at a glance whether it is listening will read the feature as
 * either broken or sinister. So each state differs in more than one channel:
 *
 *   off        slashed glyph, quiet surface        -- a different shape, not a dimmer colour
 *   armed      accent outline, slow breath          -- present, not demanding
 *   capturing  filled accent, ring pulsing outward  -- the loudest thing in the composer
 *   suspended  dimmed, no motion                    -- visibly stood down
 *
 * Shape carries `off` because colour alone would leave a colour-blind student
 * with two indistinguishable quiet buttons, and `off` is the state whose
 * misreading matters most. */
.btn-mic { flex: 0 0 auto; width: 42px; padding: 0; }

/* The slash only exists when muted. */
.mic-slash { display: none; }
.btn-mic.is-off .mic-slash { display: inline; }

/* Armed: listening, and saying so without competing with the send button.
 * An outline and a slow breath, against the filled accent of a live capture. */
.btn-mic.is-armed {
  --btn-fg: var(--primary);
  box-shadow: inset 0 0 0 1px var(--primary-line);
}

.btn-mic.is-armed::after {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  box-shadow: inset 0 0 0 1px var(--primary);
  animation: mic-breathe 2.8s var(--ease) infinite;
  pointer-events: none;
}

.btn-mic.is-live {
  --btn-bg: var(--primary);
  --btn-fg: var(--primary-foreground);
  box-shadow: var(--shadow-glow);
}

.btn-mic.is-live::after {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  box-shadow: 0 0 0 1px var(--primary);
  animation: mic-pulse 1.6s var(--ease) infinite;
  pointer-events: none;
}

/* Stood down while the tutor is talking. Deliberately inert: no pulse, no
 * breath, because the point of the state is that nothing is being heard. */
.btn-mic.is-suspended { opacity: 0.45; }

@keyframes mic-pulse {
  from { opacity: 0.85; transform: scale(1); }
  to   { opacity: 0; transform: scale(1.42); }
}

@keyframes mic-breathe {
  0%, 100% { opacity: 0.15; }
  50%      { opacity: 0.9; }
}

/* Motion is the redundant channel here, never the only one: every state is also
 * a fill, a glyph and an accessible name. Dropping it costs nothing. */
@media (prefers-reduced-motion: reduce) {
  .btn-mic.is-live::after { animation: none; opacity: 0.85; }
  .btn-mic.is-armed::after { animation: none; opacity: 0.6; }
}

/* The wake toggle: the mute control, and the only place the state is written in
 * words. Small, quiet, and never the thing you notice first -- but a student who
 * wants to know whether the microphone is open should never have to interpret an
 * icon to find out. */
.wake {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  margin-inline-start: auto;
  padding: 5px 10px 5px 8px;
  background: none;
  border: 0;
  border-radius: 999px;
  box-shadow: inset 0 0 0 1px var(--border);
  color: var(--muted-foreground);
  font-size: 12px;
  font-weight: 550;
  transition-property: color, box-shadow;
  transition-duration: 140ms;
  transition-timing-function: ease-out;
}

.wake:hover:not(:disabled) { color: var(--foreground-2); box-shadow: inset 0 0 0 1px var(--border-strong); }
.wake:disabled { opacity: 0.5; cursor: not-allowed; }

.wake.is-on { color: var(--primary); box-shadow: inset 0 0 0 1px var(--primary-line); }

.wake-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--muted-foreground);
  transition: background-color 140ms ease-out;
}

.wake.is-on .wake-dot {
  background: var(--primary);
  animation: mic-breathe 2.8s var(--ease) infinite;
}

@media (prefers-reduced-motion: reduce) {
  .wake.is-on .wake-dot { animation: none; }
}

/* A play or arrow glyph sits right of its own optical centre, so a trailing
 * icon needs slightly less padding on its side than the text side. */
.btn-icon-end { padding-inline: 18px 15px; }

/* Tabs, APG pattern. The selected tab is a filled surface rather than an
 * underline, so selection survives without colour. */
.tabs {
  display: inline-flex;
  gap: 3px;
  margin-bottom: 24px;
  padding: 3px;
  background: oklch(1 0 0 / 0.04);
  border-radius: var(--radius);
  box-shadow: inset 0 0 0 1px var(--border);
}

.tab {
  padding: 7px 15px;
  background: transparent;
  border: 0;
  border-radius: 10px;
  color: var(--muted-foreground);
  font-size: 13.5px;
  font-weight: 550;
  min-height: 34px;
  transition-property: color, background-color;
  transition-duration: 140ms;
  transition-timing-function: ease-out;
}

.tab:hover { color: var(--foreground); }
.tab.is-active { background: var(--muted); color: var(--foreground); box-shadow: var(--shadow-sm); }

/* ------------------------------------------------------------------- fields */
.field + .field { margin-top: 20px; }

/* A class, not `.field > label`: the drop zone is itself a <label> for the same
 * input, and an element selector wins on specificity and would force it back to
 * display:block, collapsing its stacked lines onto one. */
.field-label {
  display: block;
  margin-bottom: 7px;
  color: var(--foreground-2);
  font-size: 13px;
  font-weight: 560;
}

.field-hint {
  margin: 0 0 9px;
  color: var(--muted-foreground);
  font-size: 12.5px;
  line-height: 1.5;
  text-wrap: pretty;
}

input, textarea {
  width: 100%;
  padding: 11px 14px;
  background: oklch(0 0 0 / 0.24);
  color: var(--foreground);
  border: 1px solid var(--input);
  border-radius: var(--radius);
  font-family: var(--sans);
  /* 16px stops iOS Safari zooming the viewport on focus. */
  font-size: 16px;
  line-height: 1.5;
  transition-property: border-color, box-shadow, background-color;
  transition-duration: 140ms;
  transition-timing-function: ease-out;
}

@media (min-width: 640px) { input, textarea { font-size: 14.5px; } }

input.mono, textarea.mono, .review-lines input {
  font-family: var(--mono);
  letter-spacing: -0.01em;
}

textarea { resize: vertical; min-height: 118px; line-height: 1.65; }

/* Placeholders here are worked examples of the notation rather than labels
 * (every field has a visible <label>), so they are held to the same Lc 60 the
 * rest of the non-body text meets instead of faded into decoration. */
input::placeholder, textarea::placeholder { color: var(--muted-foreground); opacity: 1; }

/* Brighter than --input, not dimmer. --border-strong is a decorative hairline
 * and sits far below --input, so reusing it here would dim the border on hover. */
input:hover, textarea:hover { border-color: var(--input-hover); }

input:focus, textarea:focus {
  outline: none;
  background: oklch(0 0 0 / 0.32);
  border-color: var(--primary-line);
  box-shadow: 0 0 0 3px var(--primary-soft);
}

form > .btn { margin-top: 24px; }

/* ---------------------------------------------------------------- drop zone */
.drop {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 5px;
  min-height: 168px;
  padding: 30px 24px;
  background: oklch(0 0 0 / 0.18);
  border: 1px dashed var(--input);
  border-radius: var(--radius-lg);
  text-align: center;
  cursor: pointer;
  transition-property: border-color, background-color, color;
  transition-duration: 150ms;
  transition-timing-function: ease-out;
}

.drop:hover, .drop.is-over {
  background: var(--primary-soft);
  border-color: var(--primary-line);
  border-style: solid;
}

.drop-icon { display: block; color: var(--muted-foreground); transition: color 150ms ease-out; }
.drop:hover .drop-icon, .drop.is-over .drop-icon { color: var(--primary); }
.drop-text { color: var(--foreground-2); font-size: 14px; font-weight: 540; }
.drop-sub { color: var(--muted-foreground); font-size: 12.5px; }

/* The real input is visually hidden, so its focus ring has to land on the
 * label that stands in for it. */
#photo-file:focus-visible + .drop { outline: 2px solid var(--ring); outline-offset: 2px; }

.review { margin-top: 26px; padding-top: 26px; border-top: 1px solid var(--border); }
.review-lines { display: grid; gap: 8px; margin: 14px 0 20px; }
.review-lines input { font-size: 14px; }
.review-problem { font-weight: 600; }
/* The steps are subordinate to the problem, so they sit one step in. */
.review-step { width: calc(100% - 18px); margin-inline-start: 18px; }

.err {
  margin: 18px 0 0;
  padding: 11px 15px;
  background: var(--primary-soft);
  border-inline-start: 2px solid var(--primary);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  /* Full ink, not --foreground-2: on the coral tint that step measures Lc 73.7,
   * just under the body floor, and an error message is the last text in the app
   * that should be hard to read. */
  color: var(--foreground);
  font-size: 13.5px;
}

.err:empty { display: none; }

/* ---------------------------------------------------------------- diagnosis */
.diagnosis { overflow: hidden; }

.diagnosis.is-pending {
  display: flex;
  align-items: center;
  gap: 12px;
  color: var(--muted-foreground);
}

.diagnosis.is-pending p { margin: 0; font-size: 14.5px; }

.diagnosis h1 {
  margin: 0;
  max-width: 26ch;
  font-size: clamp(25px, 3.2vw, 33px);
  font-weight: 640;
  line-height: 1.12;
  letter-spacing: -0.026em;
  text-wrap: balance;
}

/* :not(.eyebrow) because the eyebrow is also a direct <p> child and an
 * element-bearing selector would out-specify .eyebrow's own margins. */
/* The wordmark set inside a line of type.
 *
 * Every number here comes from the artwork's measured metrics rather than from
 * eyeballing: the lettering box is 935.9 x 281.7, of which 241.7 sits above the
 * baseline (cap height, the "A") and 40 below it (the descender of the "y").
 *
 *   height      0.82em  -- so cap height lands at 0.82 x 241.7/281.7 = 0.703em,
 *                          which is the cap height of the surrounding face
 *   width       height x 935.9/281.7
 *   v-align    -0.1164em -- 0.82 x 40/281.7, dropping the box by exactly its
 *                           own descender so the logo's baseline is the line's
 *
 * Getting this from metrics rather than by nudging matters because the headline
 * is `clamp(25px, 3.2vw, 33px)`: em-relative values track it at every viewport
 * width, where a pixel nudge would only be right at one. */
.wordmark {
  display: inline-block;
  height: 0.82em;
  width: calc(0.82em * 935.9 / 281.7);
  vertical-align: -0.1164em;
  background-color: currentColor;
  mask: url(/astray-word.svg) no-repeat center / contain;
  -webkit-mask: url(/astray-word.svg) no-repeat center / contain;
}

.diagnosis > p:not(.eyebrow) {
  margin: 16px 0 0;
  max-width: 62ch;
  color: var(--foreground-2);
  font-size: 15.5px;
  line-height: 1.6;
  text-wrap: pretty;
}

/* The false rule itself, given a plaque of its own because it is the single
 * finding the whole run produces. The accent is the leading rule rather than
 * the text colour: coral has no lightness that clears the body-text floor
 * against its own tint. */
.rule {
  display: block;
  width: fit-content;
  max-width: 100%;
  margin: 20px 0 0;
  padding: 15px 18px;
  overflow-x: auto;
  background: var(--primary-soft);
  border-inline-start: 2px solid var(--primary);
  border-radius: 0 var(--radius) var(--radius) 0;
  color: var(--foreground);
  font-family: var(--mono);
  font-size: clamp(15px, 2vw, 17.5px);
  letter-spacing: -0.012em;
}

/* The solved steps, shown in place of a false rule when there was no attempt to
   diagnose. Numbered because the order is the method: these are steps to follow,
   not a list of facts. */
.solution {
  margin: 20px 0 0;
  padding: 0;
  padding-inline-start: 1.4em;
  display: grid;
  gap: 9px;
}

.solution li {
  padding-inline-start: 4px;
  color: var(--foreground-2);
  font-size: clamp(13.5px, 1.6vw, 15px);
  line-height: 1.5;
  overflow-wrap: anywhere;
}

.solution li::marker { color: var(--muted-foreground); font-size: 12px; }

.badges { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 22px; }

.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 11px;
  background: oklch(1 0 0 / 0.05);
  border-radius: var(--radius-full);
  box-shadow: inset 0 0 0 1px var(--border);
  color: var(--muted-foreground);
  font-size: 12.5px;
  font-weight: 520;
  white-space: nowrap;
  font-variant-numeric: tabular-nums;
}

/* Green means a machine checked it. The tick in the label is a second cue, so
 * the claim does not rest on colour alone. */
.badge.is-good {
  background: var(--success-soft);
  box-shadow: inset 0 0 0 1px var(--success-line);
  color: var(--foreground-2);
}

.badge.is-peers {
  background: var(--primary-soft);
  box-shadow: inset 0 0 0 1px var(--primary-line);
  color: var(--foreground-2);
}

.spinner {
  flex: 0 0 auto;
  width: 15px;
  height: 15px;
  border: 2px solid var(--border-strong);
  border-top-color: var(--primary);
  border-radius: 50%;
}

@media (prefers-reduced-motion: no-preference) {
  .spinner { animation: spin 720ms linear infinite; }
}

@keyframes spin { to { transform: rotate(360deg); } }

/* ------------------------------------------------------------------ theatre */
/* Holds the expanded two-column layout until the chat column can no longer
 * carry a readable measure, then stacks. The breakpoint comes from that, not
 * from a device width: the player needs ~560px to be watchable and the chat
 * ~348px, which stop coexisting just above 1040px. */
.theatre {
  display: grid;
  grid-template-columns: minmax(0, 1.68fr) minmax(348px, 1fr);
  gap: 22px;
  align-items: start;
}

@media (max-width: 1040px) { .theatre { grid-template-columns: minmax(0, 1fr); } }

.stage { display: grid; gap: 12px; min-width: 0; }

/* One shell around the video and its filmstrip so they read as a single device
 * rather than two stacked boxes. */
.screen {
  padding: 8px;
  background: var(--card);
  backdrop-filter: blur(14px) saturate(1.3);
  -webkit-backdrop-filter: blur(14px) saturate(1.3);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-card);
}

/* Concentric: a 26px shell with 8px padding gives an 18px inner radius. */
.player {
  position: relative;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  background: #000;
  border-radius: 18px;
  box-shadow: inset 0 0 0 1px var(--border);
}

.player video { display: block; width: 100%; height: 100%; }

.player.is-empty {
  display: grid;
  place-items: center;
  padding: 26px;
  background: oklch(0 0 0 / 0.34);
}

/* The wait is three to four minutes, so the pipeline shows the run's actual
 * reasoning instead of a spinner: each stage reports what it decided. */
.pipeline { width: min(100%, 430px); max-height: 100%; overflow-y: auto; }

.pipeline .eyebrow { margin-bottom: 12px; }

.stages { margin: 0; padding: 0; list-style: none; display: grid; gap: 2px; }

.stages li {
  display: grid;
  grid-template-columns: 15px 1fr;
  gap: 10px;
  align-items: start;
  padding: 6px 9px;
  border-radius: var(--radius-sm);
  color: var(--muted-foreground);
  font-size: 13px;
  transition-property: color, background-color;
  transition-duration: 200ms;
  transition-timing-function: ease-out;
}

.stages li.is-done { color: var(--foreground-2); }

.stages li.is-active {
  background: var(--primary-soft);
  color: var(--foreground);
  font-weight: 550;
}

.mark { text-align: center; line-height: 1.5; color: var(--muted-foreground); }
.stages li.is-done .mark { color: var(--success); }
.stages li.is-active .mark { color: var(--primary); }

.why {
  display: block;
  margin-top: 3px;
  max-width: 52ch;
  color: var(--muted-foreground);
  font-size: 12px;
  font-weight: 400;
  line-height: 1.45;
}

/* --------------------------------------------------------------------- rail */
.rail-wrap { position: relative; min-width: 0; }

.rail {
  display: flex;
  gap: 8px;
  padding: 2px 2px 6px;
  overflow-x: auto;
  scroll-behavior: smooth;
  scroll-snap-type: x proximity;
  scrollbar-width: none;
}

/* The trailing fade is the affordance for "there are more beats past the edge";
 * without it the filmstrip looks complete at whatever width it happens to be.
 *
 * It is a mask on the strip rather than a gradient to --background painted over
 * it, because the rail sits above the aurora: a fade to a flat colour would
 * read as a smudge wherever the wash behind it is not that exact colour. And it
 * is applied only when the strip actually overflows -- app.js measures that --
 * since fading the last chip when there is nothing past it is a lie. */
.rail-wrap.is-scrollable .rail {
  mask-image: linear-gradient(to right, #000 calc(100% - 52px), transparent);
  -webkit-mask-image: linear-gradient(to right, #000 calc(100% - 52px), transparent);
  padding-inline-end: 52px;
}

.rail::-webkit-scrollbar { display: none; }

.beat {
  flex: 0 0 auto;
  display: grid;
  gap: 3px;
  min-width: 156px;
  max-width: 212px;
  padding: 9px 13px;
  background: var(--card-solid);
  border: 0;
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  color: var(--muted-foreground);
  text-align: start;
  scroll-snap-align: start;
  transition-property: background-color, box-shadow, color, scale;
  transition-duration: 150ms;
  transition-timing-function: ease-out;
}

/* The timestamp lifts a step on hover as well as the fill: --muted-foreground on
 * --muted measures Lc 59.8, marginally under the floor for non-body text. */
.beat:hover:not(:disabled) { background: var(--muted); }
.beat:hover:not(:disabled) .beat-time { color: var(--foreground-2); }
.beat:active:not(:disabled) { scale: 0.96; }
.beat:disabled { opacity: 0.45; cursor: default; }

.beat-title {
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
  color: var(--foreground-2);
  font-size: 12.5px;
  font-weight: 550;
  line-height: 1.35;
  letter-spacing: -0.008em;
}

.beat-time { font-size: 11.5px; font-variant-numeric: tabular-nums; letter-spacing: 0.01em; }

/* The beat that targets the misconception is the point of the whole render.
 * Marked with a ring rather than a fill so the active state can still fill it. */
.beat.is-target { box-shadow: var(--ring-1), inset 0 0 0 1px var(--primary-line); }

.beat.is-active {
  background: var(--primary-soft-2);
  box-shadow: 0 0 0 1px var(--primary-line), 0 6px 20px -8px var(--primary-glow);
}

/* Full ink, not the accent: coral on a coral tint measures Lc 57, under the
 * floor, and the fill plus ring already say "active" without recolouring. */
.beat.is-active .beat-title, .beat.is-active .beat-time { color: var(--foreground); }

/* --------------------------------------------------------------------- chat */
.chat {
  display: flex;
  flex-direction: column;
  padding: 0;
  position: sticky;
  top: 86px;
  max-height: calc(100dvh - 130px);
  min-height: 470px;
}

@media (max-width: 1040px) { .chat { position: static; max-height: none; } }

.chat-head {
  display: flex;
  align-items: center;
  gap: 9px;
  padding: 16px 20px;
  border-bottom: 1px solid var(--border);
}

.chat-mark { display: block; flex: 0 0 auto; width: 18px; height: 18px; color: var(--foreground); }

.messages {
  flex: 1 1 auto;
  min-height: 0;
  overflow-y: auto;
  padding: 20px;
  display: grid;
  gap: 20px;
  align-content: start;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

.messages:empty { display: none; }

.msg { display: grid; gap: 6px; }
.msg.user { justify-items: end; }

.who {
  color: var(--muted-foreground);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0;
}

.msg .body { max-width: 94%; color: var(--foreground-2); font-size: 14.5px; line-height: 1.62; }

.msg.user .body {
  padding: 10px 14px;
  background: var(--muted);
  border-radius: var(--radius-lg) var(--radius-lg) var(--radius-xs) var(--radius-lg);
  box-shadow: var(--shadow-sm);
  color: var(--foreground);
}

.msg .body > *:first-child { margin-top: 0; }
.msg .body > *:last-child { margin-bottom: 0; }
.msg .body p { margin: 0 0 10px; }
.msg .body ul { margin: 0 0 10px; padding-inline-start: 20px; display: grid; gap: 7px; }
.msg .body strong { color: var(--foreground); font-weight: 620; }

.msg .body code {
  padding: 1.5px 5px;
  background: oklch(0 0 0 / 0.34);
  border-radius: var(--radius-xs);
  box-shadow: inset 0 0 0 1px var(--border);
  font-family: var(--mono);
  font-size: 0.9em;
}

/* A citation is the product's whole claim, that the tutor knows what the
 * student watched. Styled as a control because it is one: it seeks the player. */
.cite {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin: 0 1px;
  padding: 3px 10px 3px 8px;
  background: var(--primary-soft);
  border: 0;
  border-radius: var(--radius-full);
  box-shadow: inset 0 0 0 1px var(--primary-line);
  color: var(--foreground);
  font-size: 12.5px;
  font-weight: 540;
  font-variant-numeric: tabular-nums;
  vertical-align: baseline;
  transition-property: background-color, box-shadow, scale;
  transition-duration: 150ms;
  transition-timing-function: ease-out;
}

.cite:hover:not(:disabled) {
  background: var(--primary-soft-2);
  box-shadow: inset 0 0 0 1px var(--primary), 0 4px 14px -6px var(--primary-glow);
}

.cite:active:not(:disabled) { scale: 0.96; }
.cite:disabled { cursor: default; opacity: 0.6; }

/* A triangle's optical centre sits right of its geometric one. */
.cite .play { color: var(--primary); font-size: 9px; line-height: 1; transform: translateX(0.5px); }

.chat-empty { flex: 1 1 auto; display: flex; flex-direction: column; justify-content: flex-end; padding: 24px 20px; }

.chat-empty-title { margin: 0 0 6px; color: var(--foreground); font-size: 14px; font-weight: 580; }

.suggestions { display: grid; gap: 7px; margin-top: 16px; }

.suggestion {
  padding: 10px 13px;
  background: oklch(1 0 0 / 0.035);
  border: 0;
  border-radius: var(--radius);
  box-shadow: inset 0 0 0 1px var(--border);
  color: var(--foreground-2);
  font-size: 13.5px;
  text-align: start;
  transition-property: background-color, box-shadow, color, scale;
  transition-duration: 150ms;
  transition-timing-function: ease-out;
}

.suggestion:hover:not(:disabled) {
  background: oklch(1 0 0 / 0.06);
  box-shadow: inset 0 0 0 1px var(--border-strong);
  color: var(--foreground);
}

.suggestion:active:not(:disabled) { scale: 0.96; }
.suggestion:disabled { opacity: 0.45; cursor: not-allowed; }

.composer { display: flex; gap: 9px; padding: 14px 20px 0; }

#chat-hint { margin: 0; padding: 12px 20px 16px; color: var(--muted-foreground); font-size: 12px; }

/* ----------------------------------------------------------------- insights */
.stat-list { display: grid; gap: 3px; }

.stat {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 4px 16px;
  align-items: baseline;
  padding: 13px 14px;
  border-radius: var(--radius);
  transition-property: background-color;
  transition-duration: 140ms;
  transition-timing-function: ease-out;
}

.stat:hover { background: oklch(1 0 0 / 0.035); }

.stat-label { color: var(--foreground-2); font-size: 14px; line-height: 1.45; text-wrap: pretty; }

.stat-count {
  color: var(--muted-foreground);
  font-size: 12.5px;
  white-space: nowrap;
  font-variant-numeric: tabular-nums;
}

.stat-bar {
  grid-column: 1 / -1;
  height: 3px;
  min-width: 4px;
  margin-top: 5px;
  background: linear-gradient(90deg, var(--primary), oklch(0.780 0.129 29.2 / 0.42));
  border-radius: var(--radius-full);
}

/* ------------------------------------------------------- your past problems */
/* Rows are anchors, not buttons: each one is a real destination with a real
 * URL, so middle-click and "open in new tab" work, and a spoken problem that
 * scrolled off is still somewhere the student can get back to. */
.past-list { display: grid; gap: 3px; }

.past-row {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto auto;
  gap: 4px 14px;
  align-items: baseline;
  padding: 13px 14px;
  border-radius: var(--radius);
  color: inherit;
  text-decoration: none;
  transition-property: background-color;
  transition-duration: 140ms;
  transition-timing-function: ease-out;
}

.past-row:hover { background: oklch(1 0 0 / 0.035); }

.past-main { display: grid; gap: 4px; min-width: 0; }

/* The problem is the identity of the row, so it is set in the mono face the
 * student typed it in and truncated rather than wrapped -- a wrapped equation
 * loses the shape you recognise it by. */
.past-problem {
  overflow: hidden;
  color: var(--foreground-2);
  font-size: 14px;
  white-space: nowrap;
  text-overflow: ellipsis;
}

.past-sub { color: var(--muted-foreground); font-size: 12.5px; line-height: 1.45; }

.past-topic {
  padding: 4px 10px;
  background: oklch(1 0 0 / 0.05);
  border-radius: var(--radius-full);
  box-shadow: inset 0 0 0 1px var(--border);
  color: var(--muted-foreground);
  font-size: 11.5px;
  white-space: nowrap;
}

.past-when {
  color: var(--muted-foreground);
  font-size: 12px;
  white-space: nowrap;
  font-variant-numeric: tabular-nums;
}

@media (width <= 620px) {
  /* The topic chip is the first thing to go: it is a nicety beside the problem
     itself and the date, and three columns at this width truncates the problem
     to nothing. */
  .past-row { grid-template-columns: minmax(0, 1fr) auto; }
  .past-topic { display: none; }
}

/* ---------------------------------------------- the problem, on its session */
/* Load-bearing for voice. A problem that was spoken was never typed anywhere the
 * student can check, so this is the only place they can see what was heard. */
.problem-line {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 10px;
  align-items: baseline;
  margin: 0 0 14px;
  padding-inline: 2px;
}

.problem-label { color: var(--muted-foreground); font-size: 12.5px; }
.problem-line .mono { color: var(--foreground-2); font-size: 14px; }

.empty { padding: 6px 0 4px; }
.empty-title { margin: 0 0 6px; color: var(--foreground); font-size: 14.5px; font-weight: 570; }
.empty .field-hint { max-width: 52ch; margin-bottom: 0; }
.empty .btn { margin-top: 16px; }

/* ------------------------------------------------------------------- motion */
/* Staged view entrance: opacity, a short lift and a blur, chunked by semantic
 * group and offset ~90ms so the order communicates hierarchy. It runs once per
 * view mount, never on hover and never on a repeated interaction. */
/* Short on purpose. The blur makes text unreadable while it runs, so the total
 * for the last group (delay plus duration) stays inside ~0.5s. */
.enter { animation: enter 360ms var(--ease-out) both; }
.enter-1 { animation-delay: 0ms; }
.enter-2 { animation-delay: 70ms; }
.enter-3 { animation-delay: 140ms; }

@keyframes enter {
  from { opacity: 0; transform: translateY(12px); filter: blur(4px); }
  to   { opacity: 1; transform: translateY(0);    filter: blur(0); }
}

/* ---------------------------------------------------------------- utilities */
.hidden { display: none !important; }

/* The `hidden` attribute is only a UA-stylesheet `display: none`, so any author
 * rule setting `display` outranks it. `.btn` sets `display: inline-flex`, which
 * meant `<button hidden>` still rendered -- the microphone would have been
 * visible and inert on Safari and Firefox, the two browsers whose lack of
 * SpeechRecognition is the entire reason it starts hidden. */
[hidden] { display: none !important; }

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

.skip {
  position: absolute;
  inset-inline-start: 12px;
  top: 12px;
  z-index: 50;
  padding: 10px 16px;
  background: var(--popover);
  border-radius: var(--radius);
  box-shadow: var(--shadow-pop);
  color: var(--foreground);
  font-size: 13.5px;
  font-weight: 550;
  text-decoration: none;
  transform: translateY(-200%);
  transition: transform 160ms ease-out;
}

.skip:focus-visible { transform: translateY(0); }

/* Everything animated above is decorative or has a static equivalent, so all of
 * it can stop without losing information. The aurora and the beam are parked on
 * a fixed frame rather than removed, so the design still reads as designed. */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  .btn:active, .beat:active, .cite:active, .suggestion:active { scale: 1; }
  .btn-primary::after { display: none; }
  .card-lit::before { display: none; }

  .card-beam::after {
    background: conic-gradient(
      from 214deg,
      transparent 0deg 62deg,
      var(--primary-line) 84deg,
      var(--primary) 92deg,
      var(--primary-line) 100deg,
      transparent 122deg 360deg
    );
  }
}