/* Concept book: a page-turning reader for the Concepts section.
   Without JavaScript the pages sit in a swipeable row; concept-book.js turns them into a book. */
.concept-book{
  --paper:#F6F1E6;--paper-edge:#E9E1CF;--ink:#16203B;--ink-soft:#4A5672;--accent:#9A6A16;--rule:rgba(22,32,59,.14);
  margin-top:40px
}
/* fallback (no JS): horizontal row of pages */
.concept-book:not(.cb-ready){display:flex;gap:16px;overflow-x:auto;scroll-snap-type:x mandatory;padding-bottom:12px}
.concept-book:not(.cb-ready) .cb-page{flex:0 0 min(86%,440px);scroll-snap-align:start;border-radius:14px;min-height:540px}

.cb-page{box-sizing:border-box;background:var(--paper);color:var(--ink);padding:34px 36px 52px;position:relative;display:flex;flex-direction:column;overflow:hidden;
  background-image:radial-gradient(120% 90% at 0% 50%,rgba(0,0,0,.05),transparent 40%),linear-gradient(180deg,rgba(255,255,255,.35),rgba(255,255,255,0) 30%)}
.cb-page h3{font:600 clamp(24px,2.3vw,30px)/1.12 var(--display);letter-spacing:-.02em;margin:18px 0 14px;color:var(--ink)}
.cb-run{display:flex;justify-content:space-between;align-items:center;gap:12px;font:500 11px/1.4 var(--mono);letter-spacing:.16em;color:var(--accent);border-bottom:1px solid var(--rule);padding-bottom:12px}
.cb-icon{display:inline-flex;width:34px;height:34px;border-radius:50%;align-items:center;justify-content:center;background:rgba(154,106,22,.1);color:var(--accent)}
.cb-icon svg{width:18px;height:18px}
.cb-gist{font-size:17px;line-height:1.55;color:var(--ink);margin:0 0 16px}
.cb-try{margin:0 0 16px;padding:12px 14px;border-left:3px solid var(--accent);background:rgba(154,106,22,.07);font-size:15px;line-height:1.55;color:var(--ink);border-radius:0 8px 8px 0}
.cb-try span{display:block;font:600 11px/1.4 var(--mono);letter-spacing:.14em;text-transform:uppercase;color:var(--accent);margin-bottom:4px}
.cb-deep{font-size:14.5px;line-height:1.65;color:var(--ink-soft);margin:0 0 12px}
.cb-deep a,.cb-source a,.cb-link{color:#2F45A8;text-decoration:underline;text-underline-offset:3px}
.cb-source{font:12px/1.6 var(--mono);color:var(--ink-soft);margin:auto 0 0}
.cb-folio{position:absolute;left:0;right:0;bottom:16px;text-align:center;font:500 12px var(--mono);color:var(--ink-soft);letter-spacing:.1em}
.cb-lede{font-size:17px;line-height:1.6;color:var(--ink-soft);margin:0 0 18px}
.cb-toc{list-style:none;margin:0;padding:0;border-top:1px solid var(--rule)}
.cb-toc li{border-bottom:1px solid var(--rule)}
.cb-toc a{display:flex;gap:14px;align-items:baseline;padding:11px 2px;color:var(--ink);font:600 16px/1.35 var(--body);text-decoration:none}
.cb-toc a span{font:500 12px var(--mono);color:var(--accent);letter-spacing:.08em}
.cb-toc a:hover{color:var(--accent)}
.cb-hint{margin:auto 0 0;padding-top:14px;font:12px/1.6 var(--mono);color:var(--ink-soft)}
.cb-actions{display:flex;flex-direction:column;align-items:flex-start;gap:16px;margin:8px 0 0}
.cb-actions .btn-gold{color:#0a0f1e}
.cb-restart{margin:auto 0 0;align-self:flex-start;background:none;border:0;padding:8px 0;font:600 14px var(--body);color:var(--ink-soft);cursor:pointer}
.cb-restart:hover{color:var(--accent)}
.cb-page a:focus-visible,.cb-page button:focus-visible{outline:2px solid var(--accent);outline-offset:3px}

/* ---------- the book ---------- */
.cb-ready{position:relative}
.cb-stage a,.cb-stage img{-webkit-user-drag:none}
.cb-stage:focus{outline:none}.cb-stage:focus-visible{outline:2px solid var(--gold);outline-offset:8px;border-radius:16px}
.cb-stage{perspective:2200px;perspective-origin:50% 40%;touch-action:pan-y;user-select:none;-webkit-user-select:none}
.cb-book{position:relative;margin:0 auto;height:var(--cb-h,600px)}
.cb-ready[data-mode=spread] .cb-book{width:min(100%,1020px)}
.cb-ready[data-mode=single] .cb-book{width:min(100%,460px)}
.cb-book::before{content:"";position:absolute;inset:6px -6px -10px;border-radius:16px;background:rgba(0,0,0,.35);filter:blur(18px);z-index:0}
.cb-slot,.cb-leaf{position:absolute;top:0;height:100%}
.cb-ready[data-mode=spread] .cb-slot-l{left:0;width:50%}
.cb-ready[data-mode=spread] .cb-slot-r,.cb-ready[data-mode=spread] .cb-leaf{left:50%;width:50%}
.cb-ready[data-mode=single] .cb-slot-r,.cb-ready[data-mode=single] .cb-leaf{left:0;width:100%}
.cb-leaf{transform-style:preserve-3d;transform-origin:0 50%;transform:rotateY(calc(var(--a,0) * 1deg));will-change:transform}
.cb-leaf.cb-anim{transition:transform .62s cubic-bezier(.3,.1,.2,1)}
.cb-leaf.cb-anim.cb-fast{transition-duration:.42s}
.cb-face{position:absolute;inset:0;backface-visibility:hidden;-webkit-backface-visibility:hidden;overflow:hidden}
.cb-face>.cb-page,.cb-slot>.cb-page{position:absolute;inset:0;height:100%}
.cb-back{transform:rotateY(180deg)}
/* page edges and spine */
.cb-ready[data-mode=spread] .cb-slot-l .cb-page,.cb-ready[data-mode=spread] .cb-back .cb-page{border-radius:14px 0 0 14px;
  background-image:linear-gradient(270deg,rgba(0,0,0,.14),rgba(0,0,0,0) 9%),linear-gradient(180deg,rgba(255,255,255,.35),rgba(255,255,255,0) 30%)}
.cb-ready[data-mode=spread] .cb-slot-r .cb-page,.cb-ready[data-mode=spread] .cb-front .cb-page{border-radius:0 14px 14px 0;
  background-image:linear-gradient(90deg,rgba(0,0,0,.16),rgba(0,0,0,0) 8%),linear-gradient(180deg,rgba(255,255,255,.35),rgba(255,255,255,0) 30%)}
.cb-ready[data-mode=single] .cb-page{border-radius:4px 14px 14px 4px;
  background-image:linear-gradient(90deg,rgba(0,0,0,.12),rgba(0,0,0,0) 6%),linear-gradient(180deg,rgba(255,255,255,.35),rgba(255,255,255,0) 30%)}
.cb-ready[data-mode=single] .cb-slot-r .cb-page{box-shadow:inset 0 0 0 1px rgba(0,0,0,.04)}
.cb-ready[data-mode=single] .cb-book{box-shadow:4px 4px 0 -1px var(--paper-edge,#E9E1CF),8px 8px 0 -2px #DCD2BC;border-radius:4px 14px 14px 4px}
/* light that rolls across a turning page */
.cb-face::after{content:"";position:absolute;inset:0;pointer-events:none;opacity:var(--shade,0);transition:opacity .2s}
.cb-front::after{background:linear-gradient(90deg,rgba(0,0,0,.22),rgba(0,0,0,.04) 60%,rgba(255,255,255,.18))}
.cb-back::after{background:linear-gradient(270deg,rgba(0,0,0,.22),rgba(0,0,0,.04) 60%,rgba(255,255,255,.18))}
.cb-leaf.cb-anim .cb-face::after{opacity:0;transition:opacity .62s}
.cb-curl{position:absolute;right:0;bottom:0;width:44px;height:44px;background:linear-gradient(225deg,transparent 50%,rgba(0,0,0,.08) 52%,#E4DAC4 60%,#F6F1E6 100%);border-radius:0 0 14px 0;pointer-events:none;opacity:.9}

.cb-controls{display:flex;align-items:center;justify-content:center;gap:18px;margin:26px auto 0}
.cb-btn{width:46px;height:46px;border-radius:50%;border:1px solid rgba(245,242,234,.3);background:transparent;color:var(--text);font-size:20px;cursor:pointer;display:inline-flex;align-items:center;justify-content:center}
.cb-btn:hover:not(:disabled){border-color:var(--gold);color:var(--gold)}
.cb-btn:disabled{opacity:.3;cursor:default}
.cb-status{min-width:170px;text-align:center;font:500 13px/1.4 var(--mono);color:var(--slate);letter-spacing:.06em}
.cb-dots{display:flex;gap:7px;justify-content:center;margin-top:12px}
.cb-dots button{width:8px;height:8px;padding:0;border-radius:50%;border:0;background:rgba(245,242,234,.25);cursor:pointer}
.cb-dots button[aria-current=true]{background:var(--gold);width:22px;border-radius:5px}
html[data-theme=light] .cb-btn{border-color:rgba(21,32,59,.3);color:#15203B}
html[data-theme=light] .cb-dots button{background:rgba(21,32,59,.2)}
html[data-theme=light] .cb-book::before{background:rgba(21,32,59,.22)}

@media(max-width:520px){
  .cb-page{padding:26px 24px 46px}
  .cb-page h3{font-size:23px;margin:14px 0 12px}
  .cb-gist{font-size:16px}
  .cb-deep{font-size:14px}
  .cb-toc a{padding:9px 2px;font-size:15px}
  .cb-lede{font-size:16px;margin-bottom:14px}
}
@media(prefers-reduced-motion:reduce){.cb-leaf.cb-anim{transition-duration:.01s}}