:root { --ink:#18323a; --muted:#6e7f82; --paper:#f4f0e7; --teal:#176b66; --orange:#f08058; }
* { box-sizing:border-box; }
html { background:var(--paper); }
body { margin:0; color:var(--ink); background:radial-gradient(circle at 16% 5%,rgba(240,128,88,.11),transparent 28%),radial-gradient(circle at 92% 40%,rgba(23,107,102,.1),transparent 28%),var(--paper); font-family:Arial,"PingFang SC","Microsoft YaHei",sans-serif; -webkit-tap-highlight-color:transparent; overscroll-behavior:none; }
button,select { font:inherit; }
button { cursor:pointer; }
.app-shell { width:min(100%,560px); min-height:100dvh; margin:0 auto; padding:calc(20px + env(safe-area-inset-top)) 18px calc(22px + env(safe-area-inset-bottom)); display:flex; flex-direction:column; overflow:hidden; }
.topbar { display:flex; align-items:center; justify-content:space-between; }
.eyebrow { margin:0 0 4px; color:var(--teal); font-size:11px; font-weight:800; letter-spacing:.12em; }
h1 { margin:0; font-family:Georgia,"Songti SC",serif; font-size:28px; letter-spacing:-.03em; }
.round-button { width:42px; height:42px; border:1px solid rgba(24,50,58,.12); border-radius:50%; color:var(--ink); background:rgba(255,255,255,.54); font-weight:800; }
.progress-panel { margin-top:16px; }
.progress-copy { display:flex; justify-content:space-between; color:var(--muted); font-size:12px; }
.progress-copy strong { color:var(--ink); }
.progress-track { height:5px; margin-top:8px; overflow:hidden; border-radius:999px; background:rgba(24,50,58,.1); }
.progress-track span { display:block; width:0; height:100%; border-radius:inherit; background:linear-gradient(90deg,var(--teal),#5da89b); transition:width .3s ease; }
.chapter-tabs { display:flex; gap:8px; margin:16px -18px 0; padding:0 18px 3px; overflow-x:auto; scrollbar-width:none; }
.chapter-tabs::-webkit-scrollbar { display:none; }
.chapter-tabs button { flex:0 0 auto; padding:8px 13px; border:1px solid rgba(24,50,58,.1); border-radius:999px; color:var(--muted); background:rgba(255,255,255,.43); font-size:12px; }
.chapter-tabs button.active { border-color:var(--teal); color:white; background:var(--teal); }
.filter-row { display:flex; align-items:center; justify-content:space-between; gap:12px; margin-top:9px; }
.filter-row label { min-width:0; flex:1; }
.filter-row select { width:100%; height:38px; padding:0 34px 0 12px; border:1px solid rgba(24,50,58,.1); border-radius:12px; color:var(--ink); background:rgba(255,255,255,.5); font-size:12px; text-overflow:ellipsis; }
.deck-count { flex:0 0 auto; color:var(--muted); font-size:12px; font-weight:800; }
.study-area { flex:1; min-height:0; display:flex; flex-direction:column; justify-content:center; padding:12px 0 9px; }
.flashcard { width:100%; height:clamp(350px,51dvh,500px); perspective:1200px; touch-action:pan-y; cursor:pointer; user-select:none; }
.card-inner { position:relative; width:100%; height:100%; transform-style:preserve-3d; transition:transform .48s cubic-bezier(.2,.72,.2,1); }
.flashcard.is-flipped .card-inner { transform:rotateY(180deg); }
.card-face { position:absolute; inset:0; display:flex; flex-direction:column; padding:25px; overflow:auto; border:1px solid rgba(24,50,58,.09); border-radius:28px; backface-visibility:hidden; -webkit-backface-visibility:hidden; box-shadow:0 22px 60px rgba(47,55,50,.12); }
.card-front { background:linear-gradient(155deg,rgba(255,255,255,.88),rgba(255,252,244,.98)); }
.card-back { color:#fffaf1; background:linear-gradient(145deg,#176b66,#104d4b); transform:rotateY(180deg); }
.card-meta { display:flex; justify-content:space-between; gap:8px; color:var(--teal); font-size:10px; font-weight:800; letter-spacing:.05em; }
.card-meta span { max-width:68%; padding:7px 10px; overflow:hidden; border-radius:999px; background:rgba(23,107,102,.09); text-overflow:ellipsis; white-space:nowrap; }
.card-meta.light { color:white; }
.card-meta.light span { background:rgba(255,255,255,.12); }
.question-block,.answer-block { margin:auto 0; }
.card-label { margin:0 0 14px; color:var(--orange); font-size:12px; font-weight:900; letter-spacing:.12em; }
.question-block h2 { max-width:420px; margin:0; font-family:Georgia,"Songti SC",serif; font-size:clamp(29px,8vw,42px); line-height:1.22; letter-spacing:-.035em; }
.card-hint { margin:20px 0 0; color:var(--muted); font-size:14px; line-height:1.7; }
.tap-hint { display:flex; align-items:center; justify-content:center; gap:8px; color:var(--muted); font-size:12px; }
.tap-icon { display:grid; width:26px; height:26px; place-items:center; border:1px solid rgba(24,50,58,.12); border-radius:50%; }
.answer-block ol { margin:0; padding-left:24px; }
.answer-block li { margin:0 0 9px; padding-left:4px; font-size:15px; line-height:1.45; }
.answer-block li::marker { color:#f8aa8c; font-weight:900; }
.mnemonic { padding:13px 15px; border:1px solid rgba(255,255,255,.16); border-radius:16px; background:rgba(255,255,255,.08); }
.mnemonic span { display:block; margin-bottom:5px; color:#b7d8d4; font-size:10px; font-weight:800; letter-spacing:.14em; }
.mnemonic strong { font-size:13px; line-height:1.5; }
.swipe-caption { display:flex; justify-content:center; gap:10px; margin-top:12px; color:var(--muted); font-size:11px; }
.controls { display:grid; grid-template-columns:50px 1fr 50px; gap:12px; }
.controls button { min-height:50px; border:1px solid rgba(24,50,58,.12); border-radius:16px; color:var(--ink); background:rgba(255,255,255,.62); font-size:20px; }
.controls button:disabled { opacity:.45; }
.controls .mastered { color:white; background:var(--orange); border-color:var(--orange); font-size:15px; font-weight:800; box-shadow:0 9px 22px rgba(240,128,88,.24); }
.controls .mastered.done { color:var(--teal); background:rgba(255,255,255,.76); border-color:rgba(23,107,102,.22); box-shadow:none; }
.controls .mastered span { margin-left:5px; }
.empty-state { padding:46px 24px; text-align:center; }
.empty-state>span { display:grid; width:56px; height:56px; margin:0 auto 18px; place-items:center; border-radius:50%; color:white; background:var(--teal); font-size:25px; }
.empty-state h2 { margin:0; font-family:Georgia,"Songti SC",serif; }
.empty-state p { color:var(--muted); }
.empty-state button { padding:11px 16px; border:0; border-radius:12px; color:white; background:var(--orange); font-weight:800; }
.panel-backdrop { position:fixed; z-index:20; inset:0; display:flex; align-items:flex-end; justify-content:center; padding:18px 18px calc(18px + env(safe-area-inset-bottom)); background:rgba(15,38,42,.35); backdrop-filter:blur(5px); }
.panel-backdrop[hidden] { display:none; }
.settings-panel { width:min(100%,520px); padding:12px 16px 24px; border:1px solid rgba(255,255,255,.55); border-radius:27px; background:#fffdf8; box-shadow:0 30px 80px rgba(18,40,42,.25); animation:rise .25s ease-out; }
.panel-handle { width:42px; height:4px; margin:0 auto 15px; border-radius:99px; background:rgba(24,50,58,.15); }
.panel-title { display:flex; align-items:center; justify-content:space-between; padding:0 4px 15px; }
.panel-title p { margin:0 0 3px; color:var(--muted); font-size:11px; font-weight:800; letter-spacing:.12em; }
.panel-title h2 { margin:0; font-family:Georgia,"Songti SC",serif; font-size:24px; }
.panel-title button { width:38px; height:38px; border:1px solid rgba(24,50,58,.1); border-radius:50%; color:var(--ink); background:#f4f0e7; font-size:22px; }
.setting-row { width:100%; display:flex; align-items:center; justify-content:space-between; margin-top:8px; padding:14px 15px; border:1px solid rgba(24,50,58,.09); border-radius:16px; color:var(--ink); background:white; text-align:left; }
.setting-row span { display:flex; flex-direction:column; gap:4px; }
.setting-row small { color:var(--muted); }
.setting-row b { display:grid; width:34px; height:34px; place-items:center; border-radius:50%; color:var(--teal); background:rgba(23,107,102,.08); }
.setting-row.selected { border-color:rgba(23,107,102,.35); background:rgba(23,107,102,.05); }
.setting-row.danger strong,.setting-row.danger b { color:#b94c3f; }
.storage-note { margin:16px 0 0; color:var(--muted); font-size:11px; text-align:center; }
.sr-only { position:absolute; width:1px; height:1px; padding:0; overflow:hidden; clip:rect(0,0,0,0); white-space:nowrap; border:0; }
@keyframes rise { from { transform:translateY(28px); opacity:0; } }
@media (max-height:700px) { .app-shell{padding-top:calc(10px + env(safe-area-inset-top));padding-bottom:calc(10px + env(safe-area-inset-bottom))}.progress-panel{margin-top:10px}.chapter-tabs{margin-top:9px}.filter-row{margin-top:6px}.study-area{padding-top:7px}.flashcard{height:340px}.card-face{padding:19px}.question-block h2{font-size:28px}.answer-block li{margin-bottom:6px;font-size:13.5px}.swipe-caption{margin-top:7px} }
@media (min-width:760px) { .app-shell{padding-top:38px}.flashcard{height:540px} }
@media (prefers-reduced-motion:reduce) { .card-inner,.progress-track span{transition:none} }