/* ============================================================
   LLM Visual Course — shared design system
   Used by every small single-concept lesson page + the hub.
   Page-specific widget CSS lives inside each page.
   ============================================================ */
:root{
  --bg:#0b1020;
  --bg-2:#0e1528;
  --panel:#131c34;
  --panel-2:#182444;
  --line:rgba(140,160,210,.14);
  --line-strong:rgba(140,160,210,.28);
  --ink:#eaf0ff;
  --muted:#93a1c4;
  --muted-2:#657297;
  --amber:#ffb454;      /* TOKENS / structure */
  --amber-deep:#f5972a;
  --cyan:#43d6c8;       /* EMBEDDINGS / VECTORS / MEMORY */
  --violet:#9d8cff;     /* ATTENTION / GENERATION */
  --rose:#ff7a8a;       /* WEIGHTS / PARAMETERS */
  --green:#6ee787;      /* TRAINING / CORRECT */
  --grid:rgba(120,150,220,.06);
  --mono:'JetBrains Mono',ui-monospace,monospace;
  --disp:'Space Grotesk',system-ui,sans-serif;
  --body:'Inter',system-ui,sans-serif;
}

*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  background:
    radial-gradient(1200px 700px at 78% -8%, rgba(157,140,255,.10), transparent 60%),
    radial-gradient(1000px 640px at 8% 12%, rgba(67,214,200,.07), transparent 55%),
    var(--bg);
  color:var(--ink);
  font-family:var(--body);
  font-size:17px;
  line-height:1.65;
  -webkit-font-smoothing:antialiased;
  overflow-x:hidden;
}
::selection{background:rgba(255,180,84,.28)}

.wrap{max-width:900px;margin:0 auto;padding:0 26px}
.wrap-wide{max-width:1040px;margin:0 auto;padding:0 26px}

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

h1,h2,h3,h4{font-family:var(--disp);font-weight:600;line-height:1.1;margin:0}
p{margin:0}
.lede{color:var(--muted);font-size:1.08rem;max-width:64ch}
.strong-ink{color:var(--ink);font-weight:500}
.amber{color:var(--amber)}
.cyan{color:var(--cyan)}
.violet{color:var(--violet)}
.rose{color:var(--rose)}
.green{color:var(--green)}
.muted{color:var(--muted)}
.mono{font-family:var(--mono)}

.eyebrow{
  font-family:var(--mono);font-size:12px;letter-spacing:.24em;
  text-transform:uppercase;color:var(--amber);
  display:inline-flex;align-items:center;gap:10px;
}
.eyebrow::before{content:"";width:26px;height:1px;background:var(--amber);opacity:.7}

/* ---------- top progress + home link ---------- */
.topbar{position:fixed;top:0;left:0;right:0;z-index:60;height:3px;background:transparent}
.topbar .fill{height:100%;width:0;background:linear-gradient(90deg,var(--amber),var(--violet));transition:width .1s linear}
.home-link{
  position:fixed;top:14px;left:16px;z-index:61;
  font-family:var(--mono);font-size:12px;letter-spacing:.04em;
  color:var(--muted-2);background:rgba(11,16,32,.6);
  border:1px solid var(--line);border-radius:8px;padding:6px 11px;
  backdrop-filter:blur(6px);
}
.home-link:hover{color:var(--amber);border-color:var(--line-strong)}

/* ---------- lesson header ---------- */
.lesson-head{padding:96px 0 26px}
.crumbs{font-family:var(--mono);font-size:12px;color:var(--muted-2);letter-spacing:.04em;margin-bottom:20px;display:flex;flex-wrap:wrap;gap:7px;align-items:center}
.crumbs a{color:var(--muted-2)}
.crumbs a:hover{color:var(--amber)}
.crumbs .sep{opacity:.5}
.crumbs .here{color:var(--muted)}
.lesson-head h1{font-size:clamp(2rem,5vw,3.1rem);letter-spacing:-.02em;margin:16px 0 18px;max-width:20ch}
.lesson-head .lede{font-size:1.14rem}
.pill-row{display:flex;gap:9px;flex-wrap:wrap;margin-top:22px}
.meta-pill{font-family:var(--mono);font-size:11px;letter-spacing:.05em;color:var(--muted);background:var(--bg-2);border:1px solid var(--line);border-radius:20px;padding:5px 12px}
.meta-pill b{color:var(--ink);font-weight:500}

/* ---------- content blocks ---------- */
section.block{padding:26px 0}
.prose{max-width:66ch}
.prose p{color:var(--muted);font-size:1.04rem}
.prose p + p{margin-top:16px}
.h-kicker{font-family:var(--mono);font-size:13px;color:var(--muted-2);letter-spacing:.1em}
.block h2{font-size:clamp(1.5rem,3.4vw,2.1rem);letter-spacing:-.015em;margin:10px 0 16px}
.block h3{font-size:1.25rem;margin:26px 0 12px}

.reveal{opacity:0;transform:translateY(20px);transition:opacity .7s ease,transform .7s ease}
.reveal.in{opacity:1;transform:none}
@media (prefers-reduced-motion: reduce){.reveal{opacity:1;transform:none}}

/* ---------- interactive stage ---------- */
.stage{
  background:linear-gradient(180deg,var(--panel),var(--bg-2));
  border:1px solid var(--line);border-radius:18px;padding:30px;
  position:relative;overflow:hidden;margin:14px 0;
}
.stage::before{content:"";position:absolute;inset:0;border-radius:18px;background:linear-gradient(180deg,rgba(255,255,255,.03),transparent 30%);pointer-events:none}
.stage-label{
  font-family:var(--mono);font-size:11.5px;letter-spacing:.2em;text-transform:uppercase;
  color:var(--muted-2);margin-bottom:22px;display:flex;justify-content:space-between;align-items:center;gap:12px;flex-wrap:wrap;
}
.stage-note{color:var(--muted);font-size:.92rem;margin-top:22px;border-top:1px solid var(--line);padding-top:18px}
.stage-note .key{font-family:var(--mono);font-size:.8rem;letter-spacing:.06em}
.stage-note .key.amber{color:var(--amber)}
.stage-note .key.violet{color:var(--violet)}
.stage-note .key.cyan{color:var(--cyan)}
.stage-note .key.rose{color:var(--rose)}

.btn{
  font-family:var(--mono);font-size:12.5px;letter-spacing:.06em;
  color:var(--ink);background:var(--panel-2);
  border:1px solid var(--line-strong);border-radius:8px;
  padding:8px 15px;cursor:pointer;transition:.18s;
  display:inline-flex;align-items:center;gap:8px;
}
.btn:hover{border-color:var(--amber);color:var(--amber)}
.btn:focus-visible{outline:2px solid var(--amber);outline-offset:2px}
.btn.play .ico{width:0;height:0;border-left:8px solid currentColor;border-top:5px solid transparent;border-bottom:5px solid transparent}
input[type=range]{width:100%;accent-color:var(--amber);height:26px;cursor:pointer}

/* ---------- callouts ---------- */
.takeaway{
  margin:26px 0;border:1px solid var(--line-strong);border-left:3px solid var(--amber);
  border-radius:12px;background:linear-gradient(180deg,rgba(255,180,84,.06),var(--bg-2));
  padding:18px 22px;
}
.takeaway .k{font-family:var(--mono);font-size:11px;letter-spacing:.16em;text-transform:uppercase;color:var(--amber);margin-bottom:8px}
.takeaway p{color:var(--ink);font-size:1.02rem}
.takeaway b{color:var(--amber);font-weight:600}

.note-box{margin:22px 0;border:1px solid var(--line);border-radius:12px;background:var(--bg-2);padding:16px 20px}
.note-box .k{font-family:var(--mono);font-size:11px;letter-spacing:.14em;text-transform:uppercase;color:var(--cyan);margin-bottom:6px}
.note-box p{color:var(--muted);font-size:.96rem}

/* myth / reality */
.myth{margin:22px 0;border:1px solid var(--line);border-radius:12px;overflow:hidden;background:rgba(11,16,32,.5)}
.myth .m-row{display:grid;grid-template-columns:82px 1fr;gap:13px;padding:13px 16px;font-size:.92rem;align-items:start}
.myth .m-row + .m-row{border-top:1px solid var(--line)}
.myth .lbl2{font-family:var(--mono);font-size:10.5px;letter-spacing:.08em;text-transform:uppercase;padding:3px 8px;border-radius:6px;text-align:center;white-space:nowrap}
.myth .m-x{background:rgba(255,122,138,.14);color:var(--rose)}
.myth .m-r{background:rgba(110,231,135,.14);color:var(--green)}
.myth .txt{color:var(--muted)}
.myth .m-row.real .txt{color:var(--ink)}

/* under-the-hood "show the numbers" reveal */
.hood{margin:22px 0;border:1px solid var(--line);border-radius:12px;overflow:hidden;background:var(--bg-2)}
.hood summary{font-family:var(--mono);font-size:12.5px;color:var(--cyan);cursor:pointer;padding:14px 18px;list-style:none;display:flex;align-items:center;gap:10px}
.hood summary::-webkit-details-marker{display:none}
.hood summary::before{content:"▸";transition:.2s;color:var(--muted-2)}
.hood[open] summary::before{transform:rotate(90deg)}
.hood .hood-body{padding:2px 18px 18px;border-top:1px solid var(--line);color:var(--muted);font-size:.94rem}
.hood .hood-body p+p{margin-top:12px}
.hood code,code.inl{font-family:var(--mono);font-size:.86em;background:rgba(157,140,255,.12);color:var(--violet);padding:2px 6px;border-radius:5px}

/* quick self-check */
.check{margin:26px 0;border:1px solid var(--line);border-radius:14px;background:var(--panel);padding:22px 24px}
.check .q{font-family:var(--disp);font-weight:600;font-size:1.08rem;margin-bottom:14px}
.check .opts{display:flex;flex-direction:column;gap:10px}
.check .opt{text-align:left;font-family:var(--body);font-size:.98rem;color:var(--muted);background:var(--bg-2);border:1px solid var(--line);border-radius:10px;padding:12px 15px;cursor:pointer;transition:.18s}
.check .opt:hover{border-color:var(--line-strong);color:var(--ink)}
.check .opt.correct{border-color:var(--green);color:var(--green);background:rgba(110,231,135,.08)}
.check .opt.wrong{border-color:var(--rose);color:var(--rose);background:rgba(255,122,138,.08)}
.check .why{margin-top:14px;font-size:.94rem;color:var(--muted);min-height:0;opacity:0;transition:.3s}
.check .why.show{opacity:1}
.check .why b{color:var(--ink)}

/* ---------- prev / next navigation ---------- */
.pager{display:grid;grid-template-columns:1fr 1fr;gap:16px;margin:56px 0 20px}
@media(max-width:600px){.pager{grid-template-columns:1fr}}
.pager a{
  border:1px solid var(--line-strong);border-radius:14px;padding:20px 22px;
  background:linear-gradient(180deg,var(--panel-2),var(--bg-2));transition:.2s;display:block;
}
.pager a:hover{border-color:var(--amber);transform:translateY(-2px)}
.pager .dir{font-family:var(--mono);font-size:11px;letter-spacing:.14em;text-transform:uppercase;color:var(--muted-2)}
.pager .ttl{font-family:var(--disp);font-weight:600;font-size:1.1rem;color:var(--ink);margin-top:7px}
.pager .next{text-align:right}
.pager .disabled{opacity:.35;pointer-events:none}

footer{padding:60px 0 100px;color:var(--muted-2);font-size:.9rem;border-top:1px solid var(--line);margin-top:30px}
footer .wrap{display:flex;flex-direction:column;gap:8px}
footer a{color:var(--muted)}
footer a:hover{color:var(--amber)}

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