/* ============================================================
   The Learning Machine — shared design system
   UNC PRIMES Neuroanalytics · neural-network teaching site
   Applies ui-ux-pro-max principles: semantic tokens, type scale,
   accessible contrast, 44px targets, reduced-motion, focus rings.
   ============================================================ */

/* ---------- Fonts (self-hosted woff2 → fully offline) ---------- */
@font-face{font-family:'Space Grotesk';font-style:normal;font-weight:500;font-display:swap;src:url('../vendor/fonts/spacegrotesk-500.woff2') format('woff2');}
@font-face{font-family:'Space Grotesk';font-style:normal;font-weight:600;font-display:swap;src:url('../vendor/fonts/spacegrotesk-600.woff2') format('woff2');}
@font-face{font-family:'Space Grotesk';font-style:normal;font-weight:700;font-display:swap;src:url('../vendor/fonts/spacegrotesk-700.woff2') format('woff2');}
@font-face{font-family:'Inter';font-style:normal;font-weight:400;font-display:swap;src:url('../vendor/fonts/inter-400.woff2') format('woff2');}
@font-face{font-family:'Inter';font-style:normal;font-weight:500;font-display:swap;src:url('../vendor/fonts/inter-500.woff2') format('woff2');}
@font-face{font-family:'Inter';font-style:normal;font-weight:600;font-display:swap;src:url('../vendor/fonts/inter-600.woff2') format('woff2');}
@font-face{font-family:'Inter';font-style:normal;font-weight:700;font-display:swap;src:url('../vendor/fonts/inter-700.woff2') format('woff2');}
@font-face{font-family:'JetBrains Mono';font-style:normal;font-weight:500;font-display:swap;src:url('../vendor/fonts/jbmono-500.woff2') format('woff2');}

/* ---------- Design tokens ---------- */
:root{
  /* surfaces (dark, layered) */
  --bg:#080b14;
  --surface-1:#0f1626;
  --surface-2:#151d33;
  --surface-3:#1c2745;
  --border:#27324f;
  --border-soft:#1e2740;

  /* text (contrast-checked on --bg) */
  --ink:#eef2ff;     /* primary  ~15:1 */
  --ink-2:#b3bedd;   /* secondary ~8:1 */
  --ink-3:#8390b4;   /* muted ~5:1 (non-essential only) */

  /* accents */
  --blue:#5b8cff;    --blue-ink:#06122e;
  --teal:#2fe6c8;    --teal-ink:#04231d;
  --purple:#b78cff;  /* neuron A */
  --orange:#ff9d54;  /* neuron B */
  --gold:#ffd45e;
  --red:#ff6b7d;
  --green:#56e08a;

  /* gradients */
  --grad-primary:linear-gradient(135deg,var(--blue),var(--teal));
  --grad-accent:linear-gradient(135deg,var(--purple),var(--blue));

  /* type scale */
  --t-12:.75rem; --t-13:.8125rem; --t-14:.875rem; --t-16:1rem;
  --t-18:1.125rem; --t-22:1.375rem; --t-28:1.75rem; --t-36:2.25rem; --t-48:3rem;

  /* spacing (4/8 rhythm) */
  --s-1:4px; --s-2:8px; --s-3:12px; --s-4:16px; --s-5:24px; --s-6:32px; --s-7:48px;

  --radius:14px; --radius-lg:20px; --radius-sm:10px;
  --shadow:0 18px 50px rgba(0,0,0,.45);
  --shadow-sm:0 6px 18px rgba(0,0,0,.35);
  --ring:0 0 0 3px rgba(91,140,255,.55);

  /* motion */
  --dur-fast:160ms; --dur:240ms; --dur-slow:380ms;
  --ease-out:cubic-bezier(.22,.61,.36,1);
  --ease-in:cubic-bezier(.55,.06,.68,.19);
}

/* ---------- Base ---------- */
*{box-sizing:border-box}
html,body{margin:0;min-height:100%}
body{
  font-family:'Inter',system-ui,-apple-system,Segoe UI,Roboto,sans-serif;
  font-size:var(--t-16); line-height:1.55; color:var(--ink);
  background:#050812;
  -webkit-font-smoothing:antialiased; text-rendering:optimizeLegibility;
  overflow-x:hidden;
  isolation:isolate;
}
h1,h2,h3,h4{font-family:'Space Grotesk',Inter,sans-serif;line-height:1.15;margin:0;letter-spacing:.2px}
h1{font-size:var(--t-36);font-weight:700}
h2{font-size:var(--t-28);font-weight:600}
h3{font-size:var(--t-18);font-weight:600}
p{margin:0}
a{color:var(--blue);text-decoration:none}
.mono{font-family:'JetBrains Mono',ui-monospace,Consolas,monospace}
.tnum{font-variant-numeric:tabular-nums}
.muted{color:var(--ink-2)}
.dim{color:var(--ink-3)}

/* ---------- Layout ---------- */
.wrap{max-width:1180px;margin:0 auto;padding:22px 26px 56px;position:relative;z-index:2}
.neural-backdrop{position:fixed;inset:0;z-index:0;pointer-events:none;overflow:hidden;background:
  linear-gradient(180deg,rgba(5,8,18,.08),rgba(5,8,18,.64) 64%,#050812),
  linear-gradient(90deg,rgba(5,8,18,.12),rgba(5,8,18,.42) 22%,rgba(5,8,18,.68) 50%,rgba(5,8,18,.42) 78%,rgba(5,8,18,.12)),
  url('neuro-lab-bg.webp') center top / cover no-repeat,
  linear-gradient(120deg,#081028 0%,#050812 42%,#061623 100%)}
.neural-backdrop::before{content:"";position:absolute;inset:0;background-image:
  linear-gradient(rgba(91,140,255,.055) 1px,transparent 1px),
  linear-gradient(90deg,rgba(91,140,255,.045) 1px,transparent 1px);
  background-size:72px 72px;mask-image:linear-gradient(180deg,rgba(0,0,0,.42),transparent 84%);opacity:.18}
.neural-backdrop::after{content:"";position:absolute;inset:0;background:
  radial-gradient(ellipse at 50% 30%,rgba(5,8,18,.24),rgba(5,8,18,.46) 45%,rgba(5,8,18,.12) 72%),
  linear-gradient(90deg,rgba(5,8,18,.18),transparent 15%,transparent 85%,rgba(5,8,18,.2)),
  linear-gradient(180deg,rgba(5,8,18,.08),transparent 35%,rgba(5,8,18,.72));
  pointer-events:none}
#neural-bg{position:absolute;inset:0;width:100%;height:100%;display:block;opacity:.34}
.central-calm{position:absolute;top:0;bottom:0;left:12%;right:12%;background:
  radial-gradient(ellipse at 50% 26%,rgba(5,8,18,.58),rgba(5,8,18,.34) 36%,transparent 70%),
  linear-gradient(90deg,transparent,rgba(5,8,18,.56) 12%,rgba(5,8,18,.78) 50%,rgba(5,8,18,.56) 88%,transparent);
  filter:blur(.2px)}
.lab-side{position:absolute;top:0;bottom:0;width:min(34vw,520px);opacity:.12;mix-blend-mode:screen;animation:labBreath 11s var(--ease-out) infinite alternate}
.lab-side.left{left:0;background:
  radial-gradient(ellipse at 17% 33%,rgba(47,230,200,.18),transparent 22%),
  radial-gradient(ellipse at 8% 52%,rgba(91,140,255,.16),transparent 30%),
  radial-gradient(ellipse at 2% 17%,rgba(255,212,94,.07),transparent 24%),
  radial-gradient(ellipse at 24% 72%,rgba(47,230,200,.16),transparent 28%),
  linear-gradient(90deg,rgba(47,230,200,.09),transparent 70%)}
.lab-side.right{right:0;background:
  radial-gradient(ellipse at 78% 25%,rgba(91,140,255,.18),transparent 25%),
  radial-gradient(ellipse at 86% 58%,rgba(47,230,200,.16),transparent 26%),
  radial-gradient(ellipse at 97% 18%,rgba(255,212,94,.06),transparent 23%),
  radial-gradient(ellipse at 72% 76%,rgba(183,140,255,.12),transparent 24%),
  linear-gradient(270deg,rgba(91,140,255,.1),transparent 70%);
  animation-delay:-3.7s}
.lab-side::before{content:"";position:absolute;inset:10% 0 8%;background:
  repeating-radial-gradient(ellipse at 18% 58%,rgba(80,216,255,.22) 0 1px,transparent 2px 10px),
  repeating-linear-gradient(112deg,transparent 0 17px,rgba(47,230,200,.12) 18px,transparent 20px),
  linear-gradient(90deg,rgba(255,255,255,.08),transparent 18%,transparent 82%,rgba(255,255,255,.04));
  mask-image:radial-gradient(ellipse at 18% 58%,#000 0 34%,transparent 68%);
  -webkit-mask-image:radial-gradient(ellipse at 18% 58%,#000 0 34%,transparent 68%);
  opacity:.22;animation:contourDrift 16s ease-in-out infinite alternate}
.lab-side.right::before{transform:scaleX(-1);mask-image:radial-gradient(ellipse at 16% 48%,#000 0 34%,transparent 68%);-webkit-mask-image:radial-gradient(ellipse at 16% 48%,#000 0 34%,transparent 68%)}
.lab-side::after{content:"";position:absolute;bottom:10%;left:6%;width:220px;height:152px;border:1px solid rgba(91,140,255,.14);border-radius:16px;background:
  linear-gradient(rgba(47,230,200,.08),rgba(91,140,255,.025)),
  linear-gradient(90deg,transparent 0 24%,rgba(255,255,255,.07) 24.5% 25%,transparent 25.5% 49%,rgba(255,255,255,.06) 49.5% 50%,transparent 50.5% 74%,rgba(255,255,255,.05) 74.5% 75%,transparent 75.5%),
  linear-gradient(0deg,transparent 0 24%,rgba(255,255,255,.05) 24.5% 25%,transparent 25.5% 49%,rgba(255,255,255,.05) 49.5% 50%,transparent 50.5% 74%,rgba(255,255,255,.04) 74.5% 75%,transparent 75.5%),
  radial-gradient(circle at 25% 31%,rgba(160,210,255,.18),transparent 16%),
  radial-gradient(circle at 70% 33%,rgba(160,210,255,.15),transparent 16%),
  radial-gradient(circle at 29% 75%,rgba(160,210,255,.12),transparent 16%),
  radial-gradient(circle at 70% 74%,rgba(160,210,255,.12),transparent 16%);
  box-shadow:inset 0 0 30px rgba(91,140,255,.07);opacity:.16}
.lab-side.right::after{left:auto;right:7%;bottom:13%}
.neural-field{position:absolute;inset:auto -10% 0 -10%;height:34%;background:
  linear-gradient(180deg,transparent,rgba(47,230,200,.055) 50%,rgba(91,140,255,.02));
  transform:skewY(-2deg);opacity:.7}
@keyframes labBreath{from{opacity:.08;transform:translateY(0) scale(1)}to{opacity:.18;transform:translateY(-10px) scale(1.025)}}
@keyframes contourDrift{from{background-position:0 0,0 0,0 0}to{background-position:28px -18px,-36px 20px,0 0}}
.row{display:flex;gap:var(--s-4)}
.grid-2{display:grid;grid-template-columns:1fr 1fr;gap:var(--s-4)}
@media(max-width:900px){.grid-2{grid-template-columns:1fr}}

/* ---------- Top bar ---------- */
.topbar{display:flex;align-items:center;justify-content:space-between;gap:var(--s-4);flex-wrap:wrap;margin-bottom:var(--s-5)}
.brand{display:flex;align-items:center;gap:var(--s-3)}
.logo{width:44px;height:44px;border-radius:12px;background:var(--grad-primary);display:grid;place-items:center;box-shadow:0 8px 24px rgba(47,230,200,.3),0 0 32px rgba(91,140,255,.16);flex:none}
.logo svg{width:28px;height:28px}
.brand .title{font-family:'Space Grotesk';font-weight:700;font-size:var(--t-18);line-height:1.1}
.brand .sub{font-size:var(--t-12);color:var(--ink-3);text-transform:uppercase;letter-spacing:.7px;margin-top:2px}
.pill{font-size:var(--t-12);color:var(--ink-2);border:1px solid rgba(102,146,255,.22);padding:7px 12px;border-radius:999px;background:rgba(7,12,26,.58);backdrop-filter:blur(10px)}

/* ---------- Card ---------- */
.card{background:linear-gradient(180deg,var(--surface-2),var(--surface-1));border:1px solid var(--border);border-radius:var(--radius-lg);padding:var(--s-4);box-shadow:var(--shadow);position:relative;overflow:hidden}
.card-h{font-size:var(--t-16);font-weight:600;font-family:'Space Grotesk';margin-bottom:2px}
.card-sub{color:var(--ink-2);font-size:var(--t-13);margin-bottom:var(--s-3)}
.eyebrow{font-size:var(--t-12);font-weight:600;letter-spacing:1.2px;text-transform:uppercase;color:var(--teal)}

/* ---------- Buttons ---------- */
.btn{font-family:'Inter';font-weight:600;font-size:var(--t-14);border:none;border-radius:12px;
  min-height:44px;padding:0 18px;display:inline-flex;align-items:center;gap:8px;cursor:pointer;
  color:var(--blue-ink);background:var(--grad-primary);box-shadow:0 8px 22px rgba(47,230,200,.28);
  transition:transform var(--dur-fast) var(--ease-out),filter var(--dur-fast),box-shadow var(--dur-fast)}
.btn:hover{transform:translateY(-2px);filter:brightness(1.05)}
.btn:active{transform:translateY(0)}
.btn.ghost{background:rgba(255,255,255,.05);color:var(--ink);border:1px solid var(--border);box-shadow:none}
.btn.ghost:hover{background:rgba(255,255,255,.09)}
.btn:disabled{opacity:.45;cursor:not-allowed;transform:none;filter:none}
.btn:focus-visible,a:focus-visible,input:focus-visible{outline:none;box-shadow:var(--ring)}

/* ---------- Range slider ---------- */
.field{display:flex;flex-direction:column;gap:8px}
.field .lab{display:flex;justify-content:space-between;align-items:baseline;font-size:var(--t-13);color:var(--ink-2)}
.field .lab b{color:var(--ink);font-family:'JetBrains Mono';font-size:var(--t-14)}
input[type=range]{-webkit-appearance:none;appearance:none;width:100%;height:8px;border-radius:999px;
  background:linear-gradient(90deg,var(--purple),var(--blue));outline:none;cursor:pointer}
input[type=range]::-webkit-slider-thumb{-webkit-appearance:none;width:24px;height:24px;border-radius:50%;
  background:#fff;border:4px solid var(--blue);box-shadow:0 4px 12px rgba(0,0,0,.5);cursor:grab;transition:transform var(--dur-fast)}
input[type=range]::-webkit-slider-thumb:active{transform:scale(1.12);cursor:grabbing}
input[type=range]::-moz-range-thumb{width:20px;height:20px;border-radius:50%;background:#fff;border:4px solid var(--blue);cursor:grab}
input[type=range]:disabled{opacity:.45;cursor:not-allowed}

/* ---------- Stat readout ---------- */
.stats{display:flex;gap:var(--s-2);flex-wrap:wrap}
.stat{flex:1;min-width:108px;background:rgba(255,255,255,.03);border:1px solid var(--border-soft);border-radius:12px;padding:9px 12px}
.stat .k{font-size:var(--t-12);color:var(--ink-3);text-transform:uppercase;letter-spacing:.6px}
.stat .v{font-size:var(--t-28);font-weight:700;font-family:'JetBrains Mono';font-variant-numeric:tabular-nums;margin-top:2px;line-height:1}

/* ---------- Guide / coach bubble ---------- */
.guide{display:flex;gap:var(--s-3);align-items:flex-start;background:linear-gradient(180deg,rgba(91,140,255,.12),rgba(47,230,200,.05));
  border:1px solid var(--border);border-radius:var(--radius);padding:13px 16px}
.guide .av{width:34px;height:34px;border-radius:10px;background:var(--grad-accent);flex:none;display:grid;place-items:center;font-size:18px}
.guide .msg{font-size:var(--t-14);color:var(--ink);line-height:1.5}
.guide .msg b{color:var(--teal)}

/* ---------- Step ticker ---------- */
.steps{display:flex;gap:7px;flex-wrap:wrap}
.step{flex:1;min-width:92px;border:1px solid var(--border-soft);border-radius:11px;padding:9px 10px;background:rgba(255,255,255,.02);transition:all var(--dur) var(--ease-out)}
.step .n{font-size:10.5px;color:var(--ink-3);letter-spacing:.6px}
.step .t{font-size:var(--t-13);font-weight:600;margin-top:2px}
.step.active{border-color:var(--teal);background:rgba(47,230,200,.14);box-shadow:inset 0 0 0 1px var(--teal),0 8px 20px rgba(47,230,200,.15)}
.step.done{border-color:rgba(86,224,138,.5)}
.step.done .t::after{content:" ✓";color:var(--green)}

/* ---------- Badges / chips ---------- */
.tag{display:inline-flex;align-items:center;gap:6px;font-size:var(--t-12);font-weight:600;padding:4px 10px;border-radius:999px;border:1px solid var(--border);color:var(--ink-2);background:rgba(255,255,255,.03)}

/* ---------- Plot svg/canvas ---------- */
svg.plot,canvas.plot{width:100%;height:auto;display:block;touch-action:none}

/* ---------- Toast ---------- */
.toast{position:fixed;left:50%;top:22px;transform:translateX(-50%) translateY(-260%);
  background:linear-gradient(135deg,var(--green),var(--teal));color:#06210f;font-weight:700;
  padding:13px 22px;border-radius:14px;box-shadow:var(--shadow);z-index:60;font-size:var(--t-16)}
.confetti{position:fixed;width:11px;height:14px;top:0;left:0;pointer-events:none;z-index:50;border-radius:2px}

/* ---------- Footer ---------- */
.foot{margin-top:var(--s-6);color:var(--ink-3);font-size:var(--t-12);text-align:center}

/* ---------- Back link ---------- */
.back{display:inline-flex;align-items:center;gap:6px;font-size:var(--t-13);color:var(--ink-2)}
.back:hover{color:var(--ink)}

/* ---------- Reduced motion ---------- */
@media (prefers-reduced-motion: reduce){
  *{animation-duration:.001ms !important;animation-iteration-count:1 !important;transition-duration:.001ms !important}
}