/* Page, slide layout and the presentation chrome (top bar, nav buttons, overlays, loader). */

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  /* One slide per screen. The page itself scrolls, which plays best with phone browsers. */
  scroll-snap-type: y mandatory;
  overflow-y: scroll;
  scrollbar-width: none;
  background: var(--bg);
  -webkit-text-size-adjust: 100%;
}
html::-webkit-scrollbar {
  display: none;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: var(--fs-body);
  line-height: 1.45;
  overscroll-behavior-y: none;
}

h1,
h2,
h3 {
  font-family: var(--font-head);
  font-weight: 700;
  line-height: 1.05;
  margin: 0;
  letter-spacing: -0.02em;
}
h1,
h2 {
  text-shadow: 3px 3px 0 var(--stamp);
}
h1 { font-size: var(--fs-h1); }
h2 { font-size: var(--fs-h2); }
h3 { font-size: var(--fs-h3); }

p { margin: 0; }

/* hidden always wins over a component's display rule. */
[hidden] {
  display: none !important;
}

code,
.mono {
  font-family: var(--font-mono);
}

button,
input {
  font: inherit;
  color: inherit;
}

:focus-visible {
  outline: 3px solid var(--sunflower);
  outline-offset: 3px;
}

/* ---------------------------------------------------------------- slides */

.slide {
  --accent: var(--coral);
  position: relative;
  min-height: 100vh;
  min-height: 100dvh;
  scroll-snap-align: start;
  scroll-snap-stop: always;
  display: flex;
  flex-direction: column;
  gap: var(--gap);
  padding: calc(var(--bar-h) + var(--gap)) var(--pad-x) calc(var(--gap) * 2);
  overflow: hidden;
}
.slide[data-accent="coral"] { --accent: var(--coral); }
.slide[data-accent="sunflower"] { --accent: var(--sunflower); }
.slide[data-accent="mint"] { --accent: var(--mint); }
.slide[data-accent="sky"] { --accent: var(--sky); }
.slide[data-accent="lilac"] { --accent: var(--lilac); }

.slide-head {
  display: flex;
  flex-direction: column;
  gap: 8px;
  max-width: 1500px;
}
.part-label {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: var(--fs-label);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent);
}

/* Where a slide's demo lives. Panels sit side by side, and stack on phones. */
.slide-body {
  flex: 1 1 auto;
  display: flex;
  gap: calc(var(--gap) * 1.5);
  align-items: center;
  justify-content: center;
  min-height: 0;
}
.panel {
  flex: 1 1 0;
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: var(--gap);
  align-items: center;
}

.title-slide .slide-body {
  flex-direction: column;
  gap: calc(var(--gap) * 1.5);
}
.title-slide h1 {
  text-align: center;
  max-width: 16ch;
  text-transform: uppercase;
  letter-spacing: -0.03em;
  text-shadow: 6px 6px 0 var(--stamp);
}
/* The plural "s" of VAEs stays small: "VAES" reads like a different acronym. */
.title-slide h1 .keep-case {
  text-transform: none;
}
.title-slide h1 .sub {
  display: block;
  margin-top: 0.35em;
  font-size: 0.42em;
  font-weight: 700;
  letter-spacing: 0;
  text-transform: none;
  text-shadow: none;
  color: var(--accent);
}

@media (max-width: 760px) {
  .slide-body {
    flex-direction: column;
    align-items: stretch;
  }
}

@media (max-height: 700px) {
  .flow-image .cat-canvas { --cat-size: 150px; }
  .bn-img .cat-canvas,
  .loss-row .cat-canvas { --cat-size: 150px; }
  .bn-diagram { width: 220px; height: 150px; }
  .s10-map,
  .s11-map,
  .s13-map { --map-size: min(40vh, 320px); }
  .formula-bar .formula { font-size: 14px; padding: 4px 8px; }
  .loss-eq { font-size: 26px; }
  .wrap-row { padding: 6px 10px; }
  .gauss-wrap,
  svg.gauss { height: min(200px, 30vh); max-height: min(200px, 30vh); }
}

/* ---------------------------------------------------------------- top bar */

/* main.js sets data-accent on <html> to the current slide's accent. */
:root[data-accent="coral"] { --accent: var(--coral); }
:root[data-accent="sunflower"] { --accent: var(--sunflower); }
:root[data-accent="mint"] { --accent: var(--mint); }
:root[data-accent="sky"] { --accent: var(--sky); }
:root[data-accent="lilac"] { --accent: var(--lilac); }

.topbar {
  position: fixed;
  inset: 0 0 auto 0;
  height: var(--bar-h);
  z-index: 20;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 10px var(--pad-x) 0;
  background: var(--bg);
  border-bottom: 3px solid var(--line);
  font-family: var(--font-mono);
  font-size: var(--fs-label);
  font-weight: 700;
  pointer-events: none;
}
.progress {
  position: absolute;
  inset: 0 0 auto 0;
  height: 8px;
  background: var(--bg-sunken);
}
.progress-fill {
  height: 100%;
  width: 0;
  background: var(--accent);
  transition: width var(--t-med) var(--ease), background-color var(--t-med) linear;
}
.topbar-part {
  color: var(--accent);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  transition: color var(--t-med) linear;
}
.topbar-right {
  display: flex;
  align-items: center;
  gap: 14px;
  flex-shrink: 0;
  color: var(--text-soft);
}
.slide-count {
  font-family: var(--font-mono);
  font-weight: 400;
}
.offline-tick {
  display: none;
  align-items: center;
  gap: 6px;
  color: var(--mint);
  font-size: calc(var(--fs-label) * 0.85);
}
.offline-tick.on {
  display: inline-flex;
}

/* ---------------------------------------------------------------- nav buttons */

.nav-buttons {
  position: fixed;
  right: max(14px, env(safe-area-inset-right));
  bottom: max(14px, env(safe-area-inset-bottom));
  z-index: 20;
  display: flex;
  flex-direction: column;
  gap: 8px;
  transition: opacity var(--t-med) linear;
}
/* Faded but still tappable: on a phone, the first tap after a pause should still move. */
.nav-buttons.idle {
  opacity: 0;
}
/* Keys don't wake them (main.js), so show them while one has keyboard focus. */
.nav-buttons:focus-within {
  opacity: 1;
}
.nav-buttons button {
  width: 48px;
  height: 48px;
  border-radius: 0;
  border: 3px solid var(--line);
  background: var(--bg-raised);
  color: var(--text);
  box-shadow: 3px 3px 0 var(--line);
  font-size: 22px;
  line-height: 1;
  cursor: pointer;
}
.nav-buttons button:hover {
  border-color: var(--accent);
}
.nav-buttons button:disabled {
  opacity: 0.35;
  cursor: default;
}

/* ---------------------------------------------------------------- overlays */

.overlay {
  position: fixed;
  inset: 0;
  z-index: 50;
  display: grid;
  place-items: center;
  padding: 24px;
  background: color-mix(in srgb, var(--bg) 92%, #24170f);
}
.overlay[hidden] {
  display: none;
}
.help-card {
  background: var(--bg-raised);
  border: 3px solid var(--line);
  border-radius: 0;
  box-shadow: 6px 6px 0 var(--line);
  padding: 32px 40px;
  max-width: 640px;
  width: 100%;
}
.help-card h2 {
  font-size: var(--fs-h3);
  margin-bottom: 16px;
}
.help-card dl {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 10px 20px;
  margin: 0;
  font-size: var(--fs-small);
}
.help-card dt {
  font-family: var(--font-mono);
  color: var(--sunflower);
}
.help-card dd {
  margin: 0;
}
kbd {
  font-family: var(--font-mono);
  padding: 1px 8px;
  border: 1px solid var(--line);
  border-bottom-width: 3px;
  border-radius: 0;
  background: var(--bg-sunken);
}

/* ---------------------------------------------------------------- loading screen */

.loader {
  z-index: 60;
  background: var(--bg);
  backdrop-filter: none;
  transition: opacity 400ms linear;
}
.loader.done {
  opacity: 0;
  pointer-events: none;
}
.loader-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
  width: min(560px, 100%);
  text-align: center;
}
.loader .mascot {
  width: 180px;
}
.loader-bar {
  width: 100%;
  height: 16px;
  border-radius: 0;
  background: var(--bg-sunken);
  border: 3px solid var(--line);
  overflow: hidden;
}
.loader-fill {
  height: 100%;
  width: 0;
  background: var(--accent);
  transition: width 150ms linear;
}
.loader-text {
  font-family: var(--font-mono);
  font-size: var(--fs-small);
  color: var(--text-soft);
  min-height: 1.5em;
}
.loader-error {
  color: var(--coral);
  font-size: var(--fs-small);
}

/* ---------------------------------------------------------------- mascot */

.mascot {
  display: block;
  height: auto;
  overflow: visible;
}
.mascot-anim .mascot-face {
  animation: bob 3.2s ease-in-out infinite;
  transform-origin: 50% 90%;
}
.mascot-anim .mascot-eyes {
  animation: blink 4.5s infinite;
  transform-origin: 50% 50%;
  transform-box: fill-box;
}
@keyframes bob {
  0%, 100% { transform: translateY(0) rotate(0); }
  50% { transform: translateY(-4px) rotate(-2deg); }
}
@keyframes blink {
  0%, 94%, 100% { transform: scaleY(1); }
  97% { transform: scaleY(0.1); }
}
@media (prefers-reduced-motion: reduce) {
  .mascot-anim .mascot-face,
  .mascot-anim .mascot-eyes {
    animation: none;
  }
  html {
    scroll-behavior: auto;
  }
}