/* ============================================================
   JEPA Playground — shared design system
   A modern, ludic, cosmic theme for an interactive course on
   self-supervised learning & world models.
   ============================================================ */

:root {
  /* Palette */
  --bg-0: #07070f;
  --bg-1: #0c0c1a;
  --bg-2: #12122a;
  --surface: rgba(255, 255, 255, 0.04);
  --surface-2: rgba(255, 255, 255, 0.07);
  --stroke: rgba(255, 255, 255, 0.10);
  --stroke-strong: rgba(255, 255, 255, 0.20);

  --ink: #eef0ff;
  --ink-dim: #aab0d6;
  --ink-faint: #7c83ad;

  /* Neon accents */
  --blue: #4f7cff;
  --cyan: #3ad5ff;
  --pink: #ff5db1;
  --magenta: #d65bff;
  --violet: #a06bff;
  --green: #3ddc97;
  --amber: #ffb347;
  --red: #ff6b6b;

  --grad-cool: linear-gradient(135deg, #4f7cff, #3ad5ff);
  --grad-hot: linear-gradient(135deg, #ff5db1, #ffb347);
  --grad-violet: linear-gradient(135deg, #a06bff, #4f7cff);
  --grad-aurora: linear-gradient(120deg, #3ad5ff, #a06bff 45%, #ff5db1 90%);

  --r-sm: 10px;
  --r-md: 16px;
  --r-lg: 24px;
  --r-xl: 34px;

  --shadow-glow: 0 0 0 1px var(--stroke), 0 20px 60px -20px rgba(80, 120, 255, 0.45);
  --shadow-soft: 0 18px 50px -24px rgba(0, 0, 0, 0.8);

  --font-display: "Space Grotesk", "Segoe UI", system-ui, sans-serif;
  --font-body: "Inter", "Segoe UI", system-ui, -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", "SFMono-Regular", ui-monospace, monospace;

  --maxw: 1180px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--font-body);
  color: var(--ink);
  background:
    radial-gradient(1200px 800px at 15% -10%, rgba(80, 120, 255, 0.18), transparent 60%),
    radial-gradient(1000px 700px at 100% 0%, rgba(214, 91, 255, 0.14), transparent 55%),
    radial-gradient(900px 900px at 50% 120%, rgba(58, 213, 255, 0.10), transparent 60%),
    var(--bg-0);
  background-attachment: fixed;
  line-height: 1.6;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

/* Animated starfield-ish grain overlay */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background-image: radial-gradient(rgba(255, 255, 255, 0.05) 1px, transparent 1px);
  background-size: 28px 28px;
  mask-image: radial-gradient(circle at 50% 30%, black, transparent 75%);
  z-index: 0;
}

a { color: var(--cyan); text-decoration: none; }
a:hover { color: var(--ink); }

h1, h2, h3, h4 { font-family: var(--font-display); font-weight: 700; line-height: 1.15; letter-spacing: -0.02em; }

.wrap { max-width: var(--maxw); margin: 0 auto; padding: 0 22px; position: relative; z-index: 1; }

/* ---------- Top navigation ---------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  backdrop-filter: blur(14px);
  background: linear-gradient(180deg, rgba(7, 7, 15, 0.85), rgba(7, 7, 15, 0.45));
  border-bottom: 1px solid var(--stroke);
}
.nav .wrap { display: flex; align-items: center; gap: 18px; height: 64px; }
.brand { display: flex; align-items: center; gap: 10px; font-family: var(--font-display); font-weight: 700; font-size: 1.05rem; }
.brand .dot {
  width: 26px; height: 26px; border-radius: 9px; background: var(--grad-aurora);
  box-shadow: 0 0 18px rgba(160, 107, 255, 0.7);
  display: inline-block; animation: spin 9s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }
.nav-links { margin-left: auto; display: flex; gap: 6px; flex-wrap: wrap; }
.nav-links a {
  color: var(--ink-dim); font-size: 0.86rem; padding: 7px 12px; border-radius: 999px;
  transition: all 0.18s ease;
}
.nav-links a:hover, .nav-links a.active { color: var(--ink); background: var(--surface-2); }

/* ---------- Buttons / chips ---------- */
.btn {
  display: inline-flex; align-items: center; gap: 9px; cursor: pointer;
  font-family: var(--font-display); font-weight: 600; font-size: 0.95rem;
  padding: 12px 22px; border-radius: 999px; border: 1px solid transparent;
  color: #050510; background: var(--grad-cool);
  transition: transform 0.15s ease, box-shadow 0.2s ease; user-select: none;
  box-shadow: 0 10px 30px -10px rgba(79, 124, 255, 0.7);
}
.btn:hover { transform: translateY(-2px); box-shadow: 0 16px 40px -12px rgba(79, 124, 255, 0.85); }
.btn:active { transform: translateY(0); }
.btn.ghost { background: var(--surface); color: var(--ink); border-color: var(--stroke-strong); box-shadow: none; }
.btn.ghost:hover { background: var(--surface-2); }
.btn.hot { background: var(--grad-hot); box-shadow: 0 10px 30px -10px rgba(255, 93, 177, 0.7); }

.chip {
  display: inline-flex; align-items: center; gap: 7px; font-size: 0.74rem; font-weight: 600;
  letter-spacing: 0.06em; text-transform: uppercase; color: var(--ink-dim);
  padding: 6px 12px; border-radius: 999px; background: var(--surface); border: 1px solid var(--stroke);
}
.chip .led { width: 8px; height: 8px; border-radius: 50%; background: var(--green); box-shadow: 0 0 10px var(--green); }

/* ---------- Cards ---------- */
.card {
  background: var(--surface);
  border: 1px solid var(--stroke);
  border-radius: var(--r-lg);
  padding: 26px;
  box-shadow: var(--shadow-soft);
  backdrop-filter: blur(6px);
}
.card.glow { box-shadow: var(--shadow-glow); }

/* ---------- Section scaffolding ---------- */
.section { padding: 72px 0; }
.eyebrow {
  font-family: var(--font-mono); font-size: 0.78rem; letter-spacing: 0.18em;
  text-transform: uppercase; color: var(--cyan); margin: 0 0 10px;
}
.section h2 { font-size: clamp(1.7rem, 3.4vw, 2.6rem); margin: 0 0 14px; }
.lead { font-size: 1.12rem; color: var(--ink-dim); max-width: 720px; }

/* ---------- Concept block layout ---------- */
.concept {
  display: grid; grid-template-columns: 1.05fr 1fr; gap: 34px; align-items: start;
  padding: 46px 0; border-top: 1px solid var(--stroke);
}
.concept.reverse { grid-template-columns: 1fr 1.05fr; }
.concept.reverse .concept-text { order: 2; }
.concept.reverse .concept-sim { order: 1; }
.concept-text h3 { font-size: 1.55rem; margin: 6px 0 12px; }
.concept-text p { color: var(--ink-dim); }
.concept-text .key {
  margin-top: 16px; padding: 14px 16px; border-radius: var(--r-md);
  background: var(--surface); border-left: 3px solid var(--violet);
  font-size: 0.96rem;
}
.concept-text .key b { color: var(--ink); }
.concept-text .analogy {
  margin-top: 16px; padding: 14px 16px; border-radius: var(--r-md);
  background: linear-gradient(120deg, rgba(255,179,71,0.10), rgba(61,220,151,0.08));
  border-left: 3px solid var(--amber); font-size: 0.96rem; color: var(--ink-dim);
}
.concept-text .analogy b { color: var(--amber); }
.concept-text .more {
  margin-top: 14px; font-size: 0.96rem; color: var(--ink-dim);
}
.concept-text details.more {
  margin-top: 14px; border: 1px solid var(--stroke); border-radius: var(--r-md);
  background: var(--surface); padding: 0 16px;
}
.concept-text details.more summary {
  cursor: pointer; padding: 12px 0; font-family: var(--font-display); font-weight: 600;
  font-size: 0.92rem; color: var(--cyan); list-style: none;
}
.concept-text details.more summary::-webkit-details-marker { display: none; }
.concept-text details.more summary::before { content: "▸ "; color: var(--cyan); }
.concept-text details.more[open] summary::before { content: "▾ "; }
.concept-text details.more p { padding-bottom: 14px; margin: 0; }
.concept-text details.more p:first-of-type { margin-top: 2px; }
.concept-num {
  font-family: var(--font-mono); font-size: 0.8rem; color: var(--ink-faint);
  letter-spacing: 0.12em;
}

@media (max-width: 880px) {
  .concept, .concept.reverse { grid-template-columns: 1fr; gap: 18px; }
  .concept.reverse .concept-text { order: 1; }
  .concept.reverse .concept-sim { order: 2; }
}

/* ---------- Simulation shell ---------- */
.sim {
  background: linear-gradient(180deg, var(--bg-2), var(--bg-1));
  border: 1px solid var(--stroke);
  border-radius: var(--r-lg);
  padding: 18px;
  box-shadow: var(--shadow-soft);
}
.sim canvas { width: 100%; display: block; border-radius: var(--r-md); background: #06060f; touch-action: none; }
.sim-bar { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; margin-top: 14px; }
.sim-title {
  display: flex; align-items: center; gap: 8px; font-family: var(--font-display);
  font-size: 0.82rem; color: var(--ink-dim); margin-bottom: 12px; letter-spacing: 0.04em;
}
.sim-title::before { content: "▶"; color: var(--cyan); font-size: 0.7rem; }

.control { display: flex; flex-direction: column; gap: 4px; min-width: 130px; flex: 1; }
.control label { font-size: 0.72rem; color: var(--ink-faint); font-family: var(--font-mono); letter-spacing: 0.04em; }
.control .val { color: var(--cyan); }
input[type="range"] {
  -webkit-appearance: none; appearance: none; height: 6px; border-radius: 999px;
  background: var(--surface-2); outline: none;
}
input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none; width: 18px; height: 18px; border-radius: 50%;
  background: var(--grad-cool); cursor: pointer; box-shadow: 0 0 12px rgba(79, 124, 255, 0.8);
}
input[type="range"]::-moz-range-thumb {
  width: 18px; height: 18px; border: none; border-radius: 50%;
  background: var(--blue); cursor: pointer;
}

.readout {
  font-family: var(--font-mono); font-size: 0.8rem; color: var(--ink-dim);
  background: rgba(0,0,0,0.3); border: 1px solid var(--stroke); border-radius: var(--r-sm);
  padding: 10px 12px; margin-top: 12px; white-space: pre-wrap;
}
.readout .ok { color: var(--green); }
.readout .warn { color: var(--amber); }
.readout .bad { color: var(--red); }

.toggle-row { display: flex; flex-wrap: wrap; gap: 8px; }
.toggle {
  cursor: pointer; user-select: none; font-size: 0.8rem; padding: 7px 13px; border-radius: 999px;
  background: var(--surface); border: 1px solid var(--stroke); color: var(--ink-dim); transition: all 0.15s;
}
.toggle.on { background: var(--grad-violet); color: #fff; border-color: transparent; box-shadow: 0 0 16px rgba(160,107,255,0.5); }

/* ---------- Journey map (home) ---------- */
.hero { padding: 90px 0 40px; text-align: center; }
.hero h1 { font-size: clamp(2.4rem, 6vw, 4.6rem); margin: 0 0 18px; }
.hero h1 .grad {
  background: var(--grad-aurora); -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent; color: transparent;
}
.hero .lead { margin: 0 auto 28px; font-size: 1.25rem; }
.hero-cta { display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }

.map { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 20px; }
.map-card {
  position: relative; display: block; padding: 24px; border-radius: var(--r-lg);
  background: var(--surface); border: 1px solid var(--stroke); overflow: hidden;
  transition: transform 0.2s ease, border-color 0.2s ease, box-shadow 0.2s ease; color: var(--ink);
}
.map-card::after {
  content: ""; position: absolute; inset: 0; border-radius: inherit; padding: 1px;
  background: var(--grad-aurora); -webkit-mask: linear-gradient(#000 0 0) content-box, linear-gradient(#000 0 0);
  -webkit-mask-composite: xor; mask-composite: exclude; opacity: 0; transition: opacity 0.2s;
}
.map-card:hover { transform: translateY(-6px); box-shadow: 0 30px 60px -30px rgba(80,120,255,0.6); color: var(--ink); }
.map-card:hover::after { opacity: 1; }
.map-card .idx {
  font-family: var(--font-mono); font-size: 2.2rem; font-weight: 700;
  background: var(--grad-aurora); -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent; line-height: 1;
}
.map-card h3 { margin: 8px 0 8px; font-size: 1.3rem; }
.map-card p { color: var(--ink-dim); font-size: 0.92rem; margin: 0; }
.map-card .tags { margin-top: 14px; display: flex; flex-wrap: wrap; gap: 6px; }
.map-card .tags span {
  font-size: 0.68rem; color: var(--ink-faint); background: var(--surface-2);
  padding: 3px 9px; border-radius: 999px; border: 1px solid var(--stroke);
}
.map-card .done-badge {
  position: absolute; top: 16px; right: 16px; font-size: 0.7rem; color: var(--green);
  display: none; align-items: center; gap: 5px; font-weight: 600;
}
.map-card.done .done-badge { display: flex; }

/* ---------- Chapter header ---------- */
.chapter-head { padding: 70px 0 30px; }
.chapter-head .kicker { color: var(--violet); font-family: var(--font-mono); letter-spacing: 0.16em; text-transform: uppercase; font-size: 0.8rem; }
.chapter-head h1 { font-size: clamp(2rem, 5vw, 3.4rem); margin: 10px 0 16px; }
.chapter-head h1 .grad { background: var(--grad-aurora); -webkit-background-clip: text; background-clip: text; -webkit-text-fill-color: transparent; }

/* ---------- Chapter footer nav ---------- */
.chapter-nav { display: flex; justify-content: space-between; gap: 14px; padding: 50px 0 90px; flex-wrap: wrap; }
.chapter-nav a { flex: 1; min-width: 220px; }

/* ---------- Challenge banner ---------- */
.challenge {
  display: flex; gap: 14px; align-items: center; padding: 16px 20px; border-radius: var(--r-md);
  background: linear-gradient(120deg, rgba(255,93,177,0.14), rgba(255,179,71,0.12));
  border: 1px solid rgba(255,93,177,0.3); margin-top: 16px;
}
.challenge .ico { font-size: 1.6rem; }
.challenge .txt { font-size: 0.95rem; color: var(--ink); }
.challenge .txt b { color: var(--amber); }

/* ---------- Glossary pills inline ---------- */
.term { border-bottom: 1px dashed var(--violet); cursor: help; color: var(--ink); }

/* ---------- Progress bar in nav ---------- */
.progress-rail { position: fixed; top: 0; left: 0; height: 3px; width: 100%; z-index: 60; background: transparent; }
.progress-rail .fill { height: 100%; width: 0; background: var(--grad-aurora); box-shadow: 0 0 12px var(--violet); transition: width 0.1s linear; }

/* ---------- Reveal-on-scroll ---------- */
.reveal { opacity: 0; transform: translateY(24px); transition: opacity 0.6s ease, transform 0.6s ease; }
.reveal.in { opacity: 1; transform: none; }

/* ---------- Footer ---------- */
.foot { border-top: 1px solid var(--stroke); padding: 40px 0 80px; color: var(--ink-faint); font-size: 0.88rem; }
.foot a { color: var(--ink-dim); }

/* ---------- Confetti canvas ---------- */
#confetti { position: fixed; inset: 0; pointer-events: none; z-index: 200; }

/* small helpers */
.center { text-align: center; }
.mt8 { margin-top: 8px; } .mt16 { margin-top: 16px; } .mt24 { margin-top: 24px; }
.mono { font-family: var(--font-mono); }
.pill-grad { background: var(--grad-violet); -webkit-background-clip: text; background-clip: text; -webkit-text-fill-color: transparent; font-weight: 700; }
.hide { display: none !important; }