/* ============ textbook reader (books.js) ============ */
:root{
  --paper:#FFFDF7; --paper-edge:#EFE8D8; --paper-ink:#1F2A37; --paper-muted:#6B7280;
  --spine:rgba(60,45,20,.18);
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){ --paper:#1A2438; --paper-edge:#0F1828; --paper-ink:#E4EDF8; --paper-muted:#93A7C0; --spine:rgba(0,0,0,.45); }
}
:root[data-theme="dark"]{ --paper:#1A2438; --paper-edge:#0F1828; --paper-ink:#E4EDF8; --paper-muted:#93A7C0; --spine:rgba(0,0,0,.45); }

/* shelf */
.folder.bk-soon{opacity:.62}
.folder.bk-soon .folder-open{display:none}
.bk-shelf-h{grid-column:1/-1;margin:22px 0 0}

/* frame */
.rd-wrap{max-width:1240px}
.rd-top{display:flex;align-items:center;gap:12px;margin-bottom:14px}
.rd-top .back-btn{margin:0}
.rd-title{flex:1;min-width:0;display:flex;flex-direction:column;line-height:1.2}
.rd-title b{font-family:Fraunces,Georgia,serif;font-size:20px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.rd-title span{font-size:13px;color:var(--muted);white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.rd-toc-btn{white-space:nowrap}

.rd-book{position:relative;perspective:2400px;--bk:var(--brand)}
.rd-book.spread{display:grid;grid-template-columns:1fr 1fr;min-height:min(760px,calc(100vh - 210px))}
.rd-book.single{display:block;min-height:calc(100vh - 230px)}
.bk-loading{padding:60px 20px;text-align:center;color:var(--muted)}
.bk-loading.error{color:var(--danger)}

/* paper */
.bk-page{position:relative;background:var(--paper);color:var(--paper-ink);border:1px solid var(--paper-edge);
  display:flex;flex-direction:column;min-height:inherit;box-shadow:var(--shadow);overflow:hidden}
.rd-book.single .bk-page{border-radius:6px 14px 14px 6px;min-height:calc(100vh - 230px)}
.bk-page.l{border-radius:14px 3px 3px 14px;border-right:none;
  background-image:linear-gradient(to left,var(--spine),transparent 7%)}
.bk-page.r{border-radius:3px 14px 14px 3px;
  background-image:linear-gradient(to right,var(--spine),transparent 7%)}
.bk-page.blank{background:var(--paper)}
.bk-in{flex:1;overflow:auto;padding:30px 34px 18px}
.bk-foot{display:flex;justify-content:space-between;align-items:center;padding:8px 22px 12px;font-size:12px;color:var(--paper-muted);border-top:1px dashed var(--paper-edge)}
.bk-page.l .bk-foot{flex-direction:row-reverse}
.bk-foot b{font-family:"JetBrains Mono",monospace;color:var(--bk)}

/* page turning */
.bk-leaf{position:absolute;top:0;bottom:0;z-index:5;transform-style:preserve-3d;pointer-events:none}
.bk-leaf.on-r{left:50%;right:0;transform-origin:left center}
.bk-leaf.on-l{left:0;right:50%;transform-origin:right center}
.bk-leaf.on-s{left:0;right:0;transform-origin:left center}
.bk-face{position:absolute;inset:0;backface-visibility:hidden;-webkit-backface-visibility:hidden;display:flex}
.bk-face > .bk-page{flex:1;min-height:100%}
.bk-face.back{transform:rotateY(180deg)}
.bk-leaf.on-r.go{animation:bkNext .62s cubic-bezier(.45,.05,.3,1) forwards}
.bk-leaf.on-l.go{animation:bkPrev .62s cubic-bezier(.45,.05,.3,1) forwards}
.bk-leaf.on-s.next.go{animation:bkSingleNext .5s ease-in forwards}
.bk-leaf.on-s.prev.go{animation:bkSinglePrev .5s ease-out forwards}
@keyframes bkNext{from{transform:rotateY(0)}to{transform:rotateY(-180deg)}}
@keyframes bkPrev{from{transform:rotateY(0)}to{transform:rotateY(180deg)}}
@keyframes bkSingleNext{from{transform:rotateY(0);opacity:1}to{transform:rotateY(-100deg);opacity:.2}}
@keyframes bkSinglePrev{from{transform:rotateY(-100deg);opacity:.2}to{transform:rotateY(0);opacity:1}}

/* nav */
.rd-nav{display:flex;align-items:center;gap:12px;margin:16px auto 6px;max-width:640px}
.rd-nav input[type=range]{flex:1;accent-color:var(--brand)}
.rd-pno{font-family:"JetBrains Mono",monospace;font-size:13px;color:var(--muted);min-width:72px;text-align:center}
.rd-arrow{min-width:52px;font-size:18px}
.rd-arrow:disabled{opacity:.35;cursor:default}

/* content */
.bk-tag{display:inline-block;font-size:12px;font-weight:700;letter-spacing:.04em;text-transform:uppercase;color:var(--bk);
  background:color-mix(in srgb,var(--bk) 12%,transparent);padding:3px 10px;border-radius:99px}
.bk-tag.big{font-size:14px;padding:5px 14px}
.bk-h{font-family:Fraunces,Georgia,serif;font-size:26px;line-height:1.15;margin:10px 0 12px}
.bk-sub-h{display:block;font-size:12px;font-weight:700;letter-spacing:.05em;text-transform:uppercase;color:var(--paper-muted);margin:16px 0 6px}
.bk-p{margin:0 0 10px;line-height:1.6}
.bk-intro{font-style:italic;color:var(--paper-muted);margin:0 0 14px;line-height:1.5}
.bk-say{border:none;background:none;cursor:pointer;font-size:15px;padding:2px 4px;margin-left:4px;border-radius:6px;opacity:.75;vertical-align:middle}
.bk-say:hover{opacity:1;background:color-mix(in srgb,var(--bk) 14%,transparent)}

/* cover */
.t-cover .bk-in{display:flex;flex-direction:column;align-items:center;justify-content:center;text-align:center;
  background:linear-gradient(160deg,color-mix(in srgb,var(--bk) 92%,#fff),color-mix(in srgb,var(--bk) 70%,#000));color:#fff;position:relative}
.bk-cover-band{position:absolute;left:0;top:0;bottom:0;width:18px;background:rgba(0,0,0,.18)}
.bk-cover-emo{font-size:92px;line-height:1;margin-bottom:18px;filter:drop-shadow(0 6px 14px rgba(0,0,0,.25))}
.bk-cover-t{font-family:Fraunces,Georgia,serif;font-size:40px;margin:0 0 8px;line-height:1.05}
.bk-cover-sub{opacity:.9;margin:0 0 22px;max-width:30ch}
.bk-cover-grade{font-family:"Bricolage Grotesque",sans-serif;font-weight:800;font-size:22px;background:rgba(255,255,255,.18);padding:6px 18px;border-radius:99px;margin:0}
.bk-cover-ham{position:absolute;bottom:18px;font-size:13px;opacity:.85;margin:0}

/* contents */
.bk-toc{list-style:none;padding:0;margin:8px 0 0;display:grid;gap:6px}
.bk-toc-row{width:100%;display:flex;align-items:center;gap:12px;text-align:left;background:none;border:1px solid var(--paper-edge);
  border-radius:12px;padding:10px 12px;color:inherit;font:inherit;cursor:pointer}
button.bk-toc-row:hover{border-color:var(--bk)}
.bk-toc .planned .bk-toc-row{opacity:.55;cursor:default}
.bk-toc-emo{font-size:22px}
.bk-toc-t{flex:1}
.bk-toc-t b{color:var(--bk);margin-right:4px}
.bk-toc-p{font-family:"JetBrains Mono",monospace;font-size:13px;color:var(--paper-muted)}
.bk-toc-p.soon{font-family:inherit;font-size:12px}

/* unit opener */
.t-opener .bk-in{background:radial-gradient(circle at 80% 10%,color-mix(in srgb,var(--bk) 16%,transparent),transparent 60%)}
.bk-open-emo{font-size:84px;line-height:1;margin:22px 0 10px}
.bk-open-t{font-family:Fraunces,Georgia,serif;font-size:34px;line-height:1.1;margin:0 0 18px}
.bk-goals{margin:0 0 12px;padding-left:20px;line-height:1.7}
.bk-chip{display:inline-block;background:var(--surface-2);border-radius:99px;padding:5px 14px;font-size:14px;margin:8px 0 0}

/* dialogue / text */
.bk-dialog{display:grid;gap:8px}
.bk-line{display:grid;grid-template-columns:minmax(80px,auto) 1fr auto;gap:10px;align-items:baseline;line-height:1.5}
.bk-line.narr{grid-template-columns:1fr auto;font-style:italic}
.bk-who{color:var(--bk);font-size:14px}
.bk-para{display:flex;gap:6px;align-items:flex-start}
.bk-para .bk-p{flex:1}
.bk-gloss{margin-top:16px;border-top:2px dotted var(--paper-edge);padding-top:4px;font-size:14px}
.bk-gloss ul{margin:0;padding-left:18px;columns:2;column-gap:24px}
.bk-gloss li{break-inside:avoid;margin-bottom:3px}

/* vocabulary */
.bk-vocab,.bk-gram{width:100%;border-collapse:collapse;font-size:15px}
.bk-vocab th,.bk-gram th{text-align:left;font-size:12px;text-transform:uppercase;letter-spacing:.04em;color:var(--paper-muted);padding:6px 8px;border-bottom:2px solid var(--bk)}
.bk-vocab td,.bk-gram td{padding:7px 8px;border-bottom:1px solid var(--paper-edge);vertical-align:middle}
.bk-vocab tr:nth-child(even) td,.bk-gram tbody tr:nth-child(even) td{background:color-mix(in srgb,var(--bk) 4%,transparent)}
.bk-v-emo{width:34px;font-size:20px;text-align:center}
.bk-v-w b{font-weight:700}
.bk-v-m,.bk-v-x{color:var(--paper-ink)}
.bk-v-x{font-size:13.5px;color:var(--paper-muted)}

/* grammar */
.bk-gram{margin:12px 0}
.bk-gram td:first-child{font-weight:600}
.bk-ex{list-style:none;padding:0;margin:12px 0;display:grid;gap:6px}
.bk-ex li{padding:8px 12px;border-left:4px solid var(--bk);background:color-mix(in srgb,var(--bk) 6%,transparent);border-radius:0 10px 10px 0}
.bk-ex-m{display:block;font-size:13.5px;color:var(--paper-muted)}
.bk-tip{margin-top:14px;padding:12px 14px;border-radius:12px;background:color-mix(in srgb,var(--star) 18%,transparent);border:1px solid color-mix(in srgb,var(--star) 45%,transparent)}
.bk-tip p{margin:4px 0 0;line-height:1.5}

/* info box */
.bk-info{border:2px dashed color-mix(in srgb,var(--bk) 40%,transparent);border-radius:16px;padding:18px 20px;background:color-mix(in srgb,var(--bk) 5%,transparent)}
.bk-info-emo{font-size:46px;line-height:1}
.bk-task{margin:12px 0 0;padding:10px 12px;background:var(--paper);border-radius:10px;border:1px solid var(--paper-edge)}

/* exercises */
.bk-instr{font-weight:600;margin:0 0 10px}
.bk-items{margin:0 0 16px;padding-left:24px;line-height:1.75;font-family:Caveat,cursive;font-size:21px;
  background-image:repeating-linear-gradient(to bottom,transparent 0 35px,var(--paper-line) 35px 36px);background-position:0 4px}
.bk-start{display:flex;align-items:center;gap:12px;flex-wrap:wrap;justify-content:space-between;padding:12px 14px;border-radius:14px;background:var(--surface-2)}
.bk-start-info{font-size:14px;color:var(--paper-muted)}
.bk-stars{color:var(--star);font-size:17px;letter-spacing:1px}
.bk-drill{margin:0 0 12px}
.bk-drill-t{display:block;margin:0 0 6px}
.bk-end{font-size:18px;color:var(--paper-muted)}
.t-end .bk-in{display:flex;flex-direction:column;align-items:center;justify-content:center;text-align:center}

@media (max-width:979px){
  .bk-in{padding:22px 18px 14px}
  .bk-h{font-size:23px}
  .bk-cover-t{font-size:32px}
  .bk-line{grid-template-columns:1fr auto}
  .bk-line .bk-who{grid-column:1/-1;margin-bottom:-6px}
  .bk-gloss ul{columns:1}
}
@media (max-width:560px){
  .rd-top{flex-wrap:wrap}
  .rd-title{order:3;flex-basis:100%}
  .rd-nav{gap:8px}
  .rd-pno{min-width:56px}
}
@media (prefers-reduced-motion: reduce){ .bk-leaf{display:none} }