/* ==========================================================================
   CAS · Introduction to NLP — design system
   styles.css : tokens, base, layout, shared components
   sections.css : per-section visuals
   ========================================================================== */

:root{
  /* surfaces */
  --bg0:#05070d;
  --bg1:#0a101c;
  --panel:rgba(148,163,184,.055);
  --panel-2:rgba(148,163,184,.085);
  --line:rgba(148,163,184,.16);
  --line-2:rgba(148,163,184,.30);
  /* text */
  --text:#e9eef7;
  --text-2:#a9b6c9;
  --text-3:#66748c;
  /* accents */
  --teal:#5eead4;
  --indigo:#818cf8;
  --violet:#a78bfa;
  --amber:#fbbf24;
  --rose:#fb7185;
  --green:#34d399;
  --sky:#38bdf8;
  /* type */
  --font-display:"Space Grotesk","Inter",-apple-system,"Segoe UI",sans-serif;
  --font-body:"Inter",-apple-system,"Segoe UI",Roboto,sans-serif;
  --font-mono:"JetBrains Mono",ui-monospace,"SF Mono",Menlo,Consolas,monospace;
  /* layout */
  --wrap:1240px;
  --radius:16px;
  --radius-s:10px;
  --sec-pad:clamp(4.5rem,9vh,7.5rem);
  --rail-w:246px;
}

*,*::before,*::after{box-sizing:border-box}
html{font-size:115%;-webkit-text-size-adjust:100%;overflow-x:clip}
html,body{margin:0;padding:0}
body{
  background:var(--bg0);
  color:var(--text);
  font-family:var(--font-body);
  font-size:1.05rem;
  line-height:1.65;
  overflow-x:clip;
  min-height:100vh;
}
/* layered backdrop: grid + glows */
body::before{
  content:"";position:fixed;inset:0;z-index:-2;pointer-events:none;
  background:
    radial-gradient(1000px 640px at 12% -6%, rgba(94,234,212,.075), transparent 62%),
    radial-gradient(1100px 720px at 96% 12%, rgba(129,140,248,.075), transparent 60%),
    radial-gradient(900px 900px at 50% 118%, rgba(167,139,250,.05), transparent 62%);
}
body::after{
  content:"";position:fixed;inset:0;z-index:-1;pointer-events:none;opacity:.5;
  background-image:
    linear-gradient(rgba(148,163,184,.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(148,163,184,.05) 1px, transparent 1px);
  background-size:56px 56px;
  mask-image:radial-gradient(1200px 800px at 50% 0%, #000 30%, transparent 85%);
  -webkit-mask-image:radial-gradient(1200px 800px at 50% 0%, #000 30%, transparent 85%);
}
::selection{background:rgba(94,234,212,.28);color:#fff}

h1,h2,h3,h4{font-family:var(--font-display);line-height:1.12;margin:0 0 .5em;letter-spacing:-.015em}
p{margin:0 0 1em}
ul,ol{margin:0;padding:0}
li{list-style:none}
button{font:inherit;color:inherit;background:none;border:0;cursor:pointer;padding:0}
[hidden]{display:none!important}
button:focus-visible,a:focus-visible,input:focus-visible,summary:focus-visible,[tabindex]:focus-visible{
  outline:2px solid var(--teal);outline-offset:3px;border-radius:6px;
}
img,svg{max-width:100%;display:block}
a{color:var(--teal);text-decoration:none}
a:hover{text-decoration:underline}

.mono{font-family:var(--font-mono);letter-spacing:.08em;font-size:.78rem;text-transform:uppercase}
.mini{font-family:var(--font-mono);font-size:.76rem;letter-spacing:.14em;text-transform:uppercase;margin:0 0 .6rem}
.micro{font-size:.85rem;margin:.6rem 0 0}
.dim{color:var(--text-3)}
.visually-hidden{position:absolute!important;width:1px;height:1px;margin:-1px;padding:0;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap;border:0}
.skip-link{position:fixed;top:-60px;left:16px;z-index:200;background:var(--teal);color:#042220;font-weight:600;padding:.55rem 1rem;border-radius:8px;transition:top .2s}
.skip-link:focus{top:12px}

.acc-teal{color:var(--teal)} .acc-violet{color:var(--violet)} .acc-amber{color:var(--amber)}
.hl-mono{font-family:var(--font-mono);color:var(--teal);background:rgba(94,234,212,.09);padding:.06em .35em;border-radius:6px}

/* ---------------------------------------------------------------- layout */
.wrap{width:100%;max-width:var(--wrap);margin-inline:auto;padding-inline:clamp(1.1rem,4vw,2.2rem)}
.section{padding-block:var(--sec-pad);position:relative;scroll-margin-top:1rem}
@media (min-width:1100px){
  body{padding-left:0;transition:padding-left .28s ease}
  body.rail-open{padding-left:var(--rail-w)}
}
.duo{display:grid;grid-template-columns:repeat(auto-fit,minmax(min(420px,100%),1fr));gap:1.2rem;align-items:start}
.sub-block{margin-top:clamp(3rem,7vh,4.6rem)}
.sub-title{font-size:clamp(1.35rem,2.6vw,1.8rem);margin-bottom:.35rem}
.sub-title::before{content:"§";color:var(--teal);font-family:var(--font-mono);font-size:.72em;margin-right:.55rem;vertical-align:.12em}

/* section header pattern */
.sec-head{margin-bottom:clamp(1.8rem,4vh,2.8rem);max-width:820px}
.sec-head.slim{margin-bottom:1.4rem}
.kicker{font-family:var(--font-mono);font-size:.8rem;letter-spacing:.18em;color:var(--teal);text-transform:uppercase;display:flex;align-items:center;gap:.8rem;margin:0 0 1.1rem}
.knum{display:inline-grid;place-items:center;min-width:2.4rem;height:1.9rem;padding-inline:.4rem;border:1px solid rgba(94,234,212,.4);border-radius:7px;color:var(--teal);background:rgba(94,234,212,.07)}
.sec-head h2{font-size:clamp(2.2rem,5vw,3.9rem);font-weight:700}
.sec-head h2 em,.hero-title .grad{font-style:normal}
.sec-head h2 em{color:transparent;background:linear-gradient(100deg,var(--teal),var(--indigo) 70%);-webkit-background-clip:text;background-clip:text}
.sec-head .lede{color:var(--text-2);font-size:1.12rem;max-width:58ch;margin:0}

/* ---------------------------------------------------------------- panels */
.panel{
  background:var(--panel);
  border:1px solid var(--line);
  border-radius:var(--radius);
  padding:clamp(1.1rem,2.6vw,1.7rem);
  position:relative;
}
.panel::before{ /* corner tick motif */
  content:"";position:absolute;top:-1px;left:-1px;width:14px;height:14px;
  border-top:2px solid var(--line-2);border-left:2px solid var(--line-2);
  border-top-left-radius:var(--radius);
}
.note-card{
  display:flex;gap:1rem;align-items:baseline;
  border:1px solid rgba(251,191,36,.28);background:rgba(251,191,36,.05);
  border-radius:var(--radius);padding:1rem 1.3rem;margin-top:1.4rem;
}
.note-card p{margin:0;color:var(--text-2)}
.note-card .mini{margin:0;white-space:nowrap}
.warn-banner{
  display:flex;gap:.8rem;align-items:flex-start;
  border:1px solid rgba(251,113,133,.45);background:rgba(251,113,133,.08);
  color:#ffd7de;border-radius:var(--radius-s);padding:.85rem 1.1rem;font-size:.92rem;
}
.good-banner{
  border:1px solid rgba(52,211,153,.4);background:rgba(52,211,153,.07);
  color:#c9f7e5;border-radius:var(--radius-s);padding:.85rem 1.1rem;font-size:.92rem;
}
.formula{
  font-family:var(--font-mono);font-size:.92rem;color:#d9e6f5;
  background:rgba(8,13,24,.75);border:1px solid var(--line);border-radius:var(--radius-s);
  padding:.7rem .95rem;overflow-x:auto;white-space:nowrap;margin:.7rem 0;
}
.formula b{color:var(--teal);font-weight:600}

/* chips & tokens */
.chip-row{display:flex;flex-wrap:wrap;gap:.45rem;margin:0 0 1rem}
.chip{
  font-size:.85rem;color:var(--text-2);border:1px solid var(--line);border-radius:999px;
  padding:.22rem .7rem;background:rgba(8,13,24,.4);white-space:nowrap;
}
.tok{
  display:inline-block;font-family:var(--font-mono);font-size:.95rem;
  border:1px solid var(--line);background:rgba(8,13,24,.6);border-radius:8px;
  padding:.34rem .7rem;white-space:nowrap;
}
.tok-wrap{display:flex;flex-wrap:wrap;gap:.45rem;align-items:center}
.tagchip{
  display:inline-block;font-family:var(--font-mono);font-size:.78rem;font-weight:600;letter-spacing:.06em;
  border:1px solid var(--line-2);border-radius:6px;padding:.14rem .45rem;white-space:nowrap;
}

/* buttons */
.btn{
  display:inline-flex;align-items:center;gap:.5rem;
  font-family:var(--font-mono);font-size:.8rem;letter-spacing:.1em;text-transform:uppercase;
  border:1px solid var(--line-2);border-radius:9px;padding:.65rem 1.15rem;
  color:var(--text);background:rgba(8,13,24,.5);transition:border-color .2s,background .2s,transform .15s;
}
.btn:hover{border-color:var(--teal);background:rgba(94,234,212,.08)}
.btn:active{transform:translateY(1px)}
.btn-accent{border-color:rgba(94,234,212,.55);background:rgba(94,234,212,.12);color:var(--teal)}
.btn[disabled]{opacity:.4;cursor:not-allowed}
.btn[aria-pressed="true"],.btn.on{border-color:var(--teal);background:rgba(94,234,212,.14);color:var(--teal)}

/* meters */
.meter{height:8px;border-radius:99px;background:rgba(148,163,184,.14);overflow:hidden;flex:1;min-width:60px}
.meter>i{display:block;height:100%;border-radius:99px;background:linear-gradient(90deg,var(--teal),var(--indigo));transition:width .5s cubic-bezier(.2,.7,.2,1)}

/* ------------------------------------------------------------------ tabs */
.tabbar{display:flex;flex-wrap:wrap;gap:.45rem;margin-bottom:1.1rem}
.tab{
  font-family:var(--font-mono);font-size:.8rem;letter-spacing:.08em;text-transform:uppercase;
  padding:.6rem 1rem;border:1px solid var(--line);border-radius:999px;color:var(--text-2);
  background:rgba(8,13,24,.45);transition:all .18s;
}
.tab:hover{border-color:var(--line-2);color:var(--text)}
.tab[aria-selected="true"]{border-color:var(--teal);color:#05231f;background:var(--teal);font-weight:600}
.tabpanel{animation:panelIn .32s cubic-bezier(.2,.7,.2,1)}
.tabpanel.out{opacity:0;transform:translateY(6px)}
@keyframes panelIn{from{opacity:0;transform:translateY(8px)}to{opacity:1;transform:none}}

/* ---------------------------------------------------------------- bridges */
.bridge{
  display:flex;flex-direction:column;align-items:center;gap:.7rem;text-align:center;
  padding:2.2rem 1.5rem;border-top:1px solid var(--line);border-bottom:1px solid var(--line);
  background:linear-gradient(180deg,rgba(94,234,212,.03),transparent);
}
.bridge p{margin:0;max-width:48ch;color:var(--text-2);font-size:1.12rem;font-style:italic}
.bridge .arw{color:var(--teal);font-size:.8rem;animation:cueDrop 2.2s ease-in-out infinite}
@keyframes cueDrop{0%,100%{transform:translateY(-3px);opacity:.4}50%{transform:translateY(3px);opacity:1}}

/* ------------------------------------------------------------ scroll spy */
.scroll-progress{position:fixed;top:0;left:0;right:0;height:2px;z-index:120;background:transparent}
#scrollFill{height:100%;width:0;background:linear-gradient(90deg,var(--teal),var(--indigo));transition:width .12s linear}

/* ------------------------------------------------------------- nav rail */
.rail{
  display:none;position:fixed;z-index:100;inset:0 auto 0 0;width:var(--rail-w);
  flex-direction:column;gap:1.4rem;padding:1.4rem 1rem;
  border-right:1px solid var(--line);background:rgba(5,8,14,.82);backdrop-filter:blur(14px);
}
@media (min-width:1100px){
  .rail{display:flex;transform:translateX(-100%);transition:transform .28s ease}
  body.rail-open .rail{transform:translateX(0)}
}
/* toggle control (desktop; mobile uses the sheet FAB) — top-right, clear of content */
.rail-toggle{
  display:none;position:fixed;top:1rem;right:1rem;z-index:120;
  align-items:center;gap:.55rem;cursor:pointer;
  font-family:var(--font-mono);font-size:.72rem;letter-spacing:.16em;
  color:var(--text-2);background:rgba(8,13,24,.85);backdrop-filter:blur(10px);
  border:1px solid var(--line-2);border-radius:9px;padding:.55rem .85rem;
  transition:color .2s,border-color .2s,background .2s;
}
.rail-toggle:hover{color:var(--teal);border-color:rgba(94,234,212,.5)}
.rail-toggle .ico{font-size:.95rem;line-height:1;color:var(--teal)}
.rail-toggle[aria-expanded="true"] .ico{color:var(--rose)}
@media (min-width:1100px){
  .rail-toggle{display:inline-flex}
}
.rail-brand{display:flex;gap:.7rem;align-items:center;color:var(--text);text-decoration:none}
.rail-brand:hover{text-decoration:none}
.brand-logo{width:2.7rem;height:2.7rem;object-fit:contain;border-radius:9px;flex:none;background:rgba(8,13,24,.5)}
.brand-logo.big{width:3.2rem;height:3.2rem}
.brand-txt{display:flex;flex-direction:column;line-height:1.15}
.brand-txt strong{font-family:var(--font-display);letter-spacing:.04em}
.brand-txt small{color:var(--text-3);font-size:.68rem;letter-spacing:.05em}
.rail-list{display:flex;flex-direction:column;gap:2px;counter-reset:rail}
.rail-list a{
  display:flex;gap:.65rem;align-items:baseline;padding:.42rem .6rem;border-radius:8px;
  color:var(--text-2);font-size:.9rem;text-decoration:none;border-left:2px solid transparent;
}
.rail-list a:hover{background:var(--panel);color:var(--text);text-decoration:none}
.rail-list a .rn{font-family:var(--font-mono);font-size:.7rem;color:var(--text-3);width:1.5rem}
.rail-list a.active{color:var(--text);background:var(--panel-2);border-left-color:var(--teal)}
.rail-list a.active .rn{color:var(--teal)}
.rail-foot{margin-top:auto;display:flex;flex-direction:column;gap:.3rem}
.rail-foot .mono{color:var(--text-3)}

/* mobile TOC */
.toc-fab{
  display:none;position:fixed;right:1rem;bottom:1rem;z-index:110;width:3.1rem;height:3.1rem;
  border-radius:50%;border:1px solid var(--line-2);background:rgba(10,16,28,.92);color:var(--teal);
  font-size:1.3rem;box-shadow:0 8px 30px rgba(0,0,0,.5);
}
.toc-sheet{position:fixed;inset:0;z-index:130}
.toc-backdrop{position:absolute;inset:0;background:rgba(3,5,10,.7);backdrop-filter:blur(4px)}
.toc-panel{
  position:absolute;left:0;top:0;bottom:0;width:min(320px,86vw);padding:1.6rem 1.3rem;
  background:var(--bg1);border-right:1px solid var(--line-2);display:flex;flex-direction:column;gap:1rem;
  animation:sheetIn .25s ease-out;overflow-y:auto;
}
@keyframes sheetIn{from{transform:translateX(-30px);opacity:0}to{transform:none;opacity:1}}
.toc-panel ol{display:flex;flex-direction:column;gap:2px;flex:1}
.toc-panel ol a{display:flex;gap:.7rem;padding:.55rem .6rem;border-radius:8px;color:var(--text-2);text-decoration:none}
.toc-panel ol a.active{background:var(--panel-2);color:var(--text)}
.toc-panel .rn{font-family:var(--font-mono);font-size:.66rem;color:var(--teal);width:1.6rem}
@media (max-width:1099px){.toc-fab{display:grid;place-items:center}}

/* ------------------------------------------------------------------ quiz */
.quiz{max-width:760px}
.quiz-top{display:flex;justify-content:space-between;align-items:center;gap:1rem;margin-bottom:1rem;flex-wrap:wrap}
.quiz-dots{display:flex;gap:.4rem}
.qdot{width:.55rem;height:.55rem;border-radius:50%;background:rgba(148,163,184,.25)}
.qdot.done{background:var(--teal)}
.qdot.now{background:var(--indigo);transform:scale(1.25)}
.quiz-q{
  border:1px solid var(--line);border-radius:var(--radius);background:var(--panel);
  padding:1.3rem 1.4rem;
}
.quiz-q legend,.quiz-q .q-text{font-weight:600;font-size:1.15rem;margin-bottom:1rem;font-family:var(--font-display)}
.q-opts{display:flex;flex-direction:column;gap:.55rem}
.q-opt{
  display:flex;gap:.8rem;align-items:flex-start;border:1px solid var(--line);border-radius:10px;
  padding:.75rem .95rem;cursor:pointer;transition:border-color .15s,background .15s;font-size:1.03rem;
}
.q-opt:hover{border-color:var(--line-2);background:var(--panel-2)}
.q-opt input{margin-top:.25rem;accent-color:var(--teal)}
.q-opt.correct{border-color:rgba(52,211,153,.7);background:rgba(52,211,153,.09)}
.q-opt.wrong{border-color:rgba(251,113,133,.7);background:rgba(251,113,133,.08)}
.q-explain{margin-top:1rem;font-size:.98rem;color:var(--text-2);border-left:3px solid var(--teal);padding:.5rem .9rem;background:rgba(94,234,212,.05);border-radius:0 8px 8px 0}
.q-foot{display:flex;justify-content:flex-end;margin-top:1.1rem}
.quiz-result{text-align:center;border:1px solid rgba(94,234,212,.4);border-radius:var(--radius);padding:2.2rem 1.4rem;background:radial-gradient(500px 240px at 50% 0%,rgba(94,234,212,.09),transparent)}
.score-ring{width:150px;height:150px;margin:0 auto 1rem}
.concept-chips{display:flex;flex-wrap:wrap;gap:.5rem;justify-content:center;max-width:640px;margin:1.2rem auto 0}
.concept-chips .chip{border-color:rgba(94,234,212,.35);color:var(--teal);background:rgba(94,234,212,.06)}
.foundation-badge{
  display:inline-block;font-family:var(--font-mono);letter-spacing:.24em;font-size:.88rem;
  color:#05231f;background:linear-gradient(100deg,var(--teal),var(--sky));
  padding:.5rem 1.2rem;border-radius:999px;margin:1.2rem 0 .4rem;box-shadow:0 0 32px rgba(94,234,212,.4);
}

/* --------------------------------------------------------------- footer */
.footer{border-top:1px solid var(--line);padding:3rem 0 2.4rem;margin-top:2rem;background:linear-gradient(180deg,transparent,rgba(94,234,212,.03))}
.footer-grid{display:flex;justify-content:space-between;gap:2rem;flex-wrap:wrap}
.f-brand{display:flex;align-items:center;gap:.7rem;font-family:var(--font-display);font-size:1.05rem;margin-bottom:.4rem}
.f-right{text-align:right}
.footer-note{margin-top:2rem;border-top:1px dashed var(--line);padding-top:1rem}

.noscript-note{position:fixed;bottom:0;left:0;right:0;z-index:300;background:#422006;color:#fde68a;padding:.8rem 1.2rem;text-align:center;font-size:.9rem}

/* ------------------------------------------------------------- reveal fx */
.js [data-reveal]{opacity:0;transform:translateY(16px)}
.js [data-reveal].revealed{opacity:1;transform:none;transition:opacity .7s cubic-bezier(.2,.7,.2,1),transform .7s cubic-bezier(.2,.7,.2,1)}
.js [data-reveal].revealed{transition-delay:var(--d,0s)}

/* ------------------------------------------------------- reduced motion */
@media (prefers-reduced-motion:reduce){
  *,*::before,*::after{animation-duration:.001s!important;animation-iteration-count:1!important;transition-duration:.001s!important}
  .bridge .arw,.scroll-cue span{animation:none!important}
  html{scroll-behavior:auto}
}
/* static mode (?static) — everything visible, animations off: for handouts/print */
.static *,.static *::before,.static *::after{animation:none!important;transition:none!important}