:root{
  --teal:#0e7c86; --teal-d:#0b646c; --blue:#1565c0; --blue-d:#0d47a1;
  --orange:#e8730c; --green:#2e9e5b; --red:#d8453a;
  --bg:#eef3f5; --card:#ffffff; --line:#e3eaed; --text:#22323a; --muted:#6b7c84;
  --ink:#1c2b32; --soft:#52646c;
  --shadow:0 1px 3px rgba(16,40,50,.08),0 6px 20px rgba(16,40,50,.06);
  --radius:14px; --maxw:1080px; --readw:760px;
}
*{box-sizing:border-box;-webkit-tap-highlight-color:transparent}
html,body{margin:0;padding:0}
body{
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;
  background:var(--bg); color:var(--text); line-height:1.7; font-size:16px;
  padding-bottom:env(safe-area-inset-bottom);
  overflow-x:hidden; word-wrap:break-word; -webkit-text-size-adjust:100%;
}
a{color:var(--teal);text-decoration:none}
button{font-family:inherit;cursor:pointer}
img{max-width:100%;height:auto}
.view{max-width:var(--maxw);margin:0 auto;padding:16px}

/* header */
.app-header{
  position:sticky;top:0;z-index:30;display:flex;align-items:center;gap:16px;
  background:linear-gradient(90deg,var(--teal),var(--blue));color:#fff;
  padding:10px 16px;box-shadow:var(--shadow);
}
.brand{display:flex;align-items:center;gap:10px;flex:1;min-width:0}
.brand-logo{width:34px;height:34px;border-radius:9px;background:rgba(255,255,255,.18);
  display:grid;place-items:center;font-weight:800;font-size:18px}
.brand-text{display:flex;flex-direction:column;min-width:0}
.brand-text strong{font-size:15px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.brand-text small{font-size:11px;opacity:.85}
.topnav{display:flex;gap:4px}
.topnav a{padding:7px 14px;border-radius:8px;color:#fff;font-size:14px;font-weight:600;opacity:.85}
.topnav a.active,.topnav a:hover{background:rgba(255,255,255,.18);opacity:1}
.subject-nav{display:flex;gap:4px}
.subj-tab{border:none;background:rgba(255,255,255,.12);color:#fff;padding:6px 12px;border-radius:8px;font-size:13px;font-weight:600;cursor:pointer;opacity:.85}
.subj-tab:hover{background:rgba(255,255,255,.22);opacity:1}
.subj-tab.active{background:#fff;color:var(--teal);opacity:1}
.header-user{display:flex;align-items:center;gap:10px;font-size:13px}
.header-user .uname{opacity:.95}
.btn-ghost{border:1px solid rgba(255,255,255,.5);background:transparent;color:#fff;
  padding:5px 12px;border-radius:8px;font-size:13px}

/* tabbar (mobile) */
.tabbar{display:none}

/* cards */
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);
  box-shadow:var(--shadow);padding:16px;margin-bottom:14px}
.card h3{margin:0 0 10px;font-size:16px}
.grid{display:grid;gap:14px}
.chapter-grid{grid-template-columns:repeat(auto-fill,minmax(240px,1fr))}
.chip{display:inline-block;background:#e8f3f4;color:var(--teal-d);border-radius:999px;
  padding:2px 10px;font-size:12px;margin:2px 4px 2px 0}

/* buttons */
.btn{border:none;border-radius:9px;padding:11px 18px;font-size:14px;font-weight:600;
  background:var(--teal);color:#fff;transition:.15s;line-height:1.2}
.btn:hover{background:var(--teal-d)}
.btn.blue{background:var(--blue)} .btn.blue:hover{background:var(--blue-d)}
.btn.ghost{background:#fff;color:var(--teal);border:1px solid var(--line)}
.btn.orange{background:var(--orange)} .btn.orange:hover{background:#cf6406}
.btn.block{width:100%}
.btn:disabled{opacity:.5;cursor:not-allowed}

/* forms */
.field{margin-bottom:14px}
.field label{display:block;font-size:13px;color:var(--muted);margin-bottom:6px}
.field input,.field select{width:100%;padding:12px;border:1px solid var(--line);border-radius:9px;font-size:16px;
  background:#fbfdfd;color:var(--ink)}
.field input:focus,.field select:focus{outline:none;border-color:var(--teal)}
.auth-wrap{max-width:380px;margin:6vh auto 0}
.center{text-align:center}
.muted{color:var(--muted)}
.row{display:flex;gap:10px;flex-wrap:wrap;align-items:center}
.spacer{flex:1}

/* study layout */
.study{display:grid;grid-template-columns:248px 1fr;gap:18px;align-items:start}
.tree{position:sticky;top:74px;max-height:calc(100vh - 90px);overflow:auto;
  background:#fff;border:1px solid var(--line);border-radius:var(--radius);padding:12px;box-shadow:var(--shadow)}
.tree .t-chapter{font-weight:700;font-size:13px;color:var(--teal-d);margin:12px 0 4px;padding-left:4px}
.tree .t-chapter:first-child{margin-top:0}
.tree a.t-sec{display:flex;align-items:center;gap:8px;padding:7px 10px;border-radius:8px;font-size:13.5px;color:var(--text)}
.tree a.t-sec:hover{background:#eef6f7}
.tree a.t-sec.active{background:var(--teal);color:#fff}
.tree a.t-sec .dot{width:7px;height:7px;border-radius:50%;background:#cfd9dd;flex:none}
.tree a.t-sec.read .dot{background:var(--green)}
.tree a.t-sub{padding:5px 10px 5px 22px;font-size:12.5px;color:var(--soft);gap:6px}
.tree a.t-sub .dot{width:5px;height:5px}

/* 阅读区：舒适排版 */
.reader{max-width:var(--readw);margin:0 auto;background:#fff;border:1px solid var(--line);
  border-radius:var(--radius);box-shadow:var(--shadow);padding:26px 28px}
.reader h2.sec-title{margin:0 0 4px;font-size:23px;color:var(--ink);line-height:1.35}
.reader .sec-meta{color:var(--muted);font-size:12.5px;margin-bottom:16px;
  padding-bottom:12px;border-bottom:1px dashed var(--line)}
.reader h3.sub{font-size:18px;margin:26px 0 10px;color:var(--blue-d);
  border-left:4px solid var(--teal);padding-left:12px;scroll-margin-top:80px;line-height:1.4}
.reader h4.sub{font-size:16px;margin:20px 0 8px;color:var(--teal-d);
  border-left:3px solid var(--orange);padding-left:10px;scroll-margin-top:80px;line-height:1.4}
.reader h5.sub{font-size:14.5px;margin:16px 0 6px;color:var(--soft);
  border-left:3px solid #cfd9dd;padding-left:10px;scroll-margin-top:80px;line-height:1.4}
.reader p{margin:0 0 14px;font-size:16px;line-height:1.9;color:var(--ink);letter-spacing:.1px}
.reader p .kw{color:var(--orange);font-weight:700}
.reader .sub-toolbar{display:flex;gap:8px;margin:10px 0 2px}
.iconbtn{border:1px solid var(--line);background:#fff;border-radius:8px;padding:5px 12px;font-size:13px;color:var(--muted)}
.iconbtn.on{color:var(--orange);border-color:var(--orange);background:#fff7f0}

/* 教材图表（内联附图，tight crop 小图，居中） */
.reader figure.inline-fig{margin:18px auto;padding:0;border:1px solid var(--line);border-radius:10px;overflow:hidden;background:#fff;max-width:560px;box-shadow:0 1px 4px rgba(0,0,0,.04)}
.reader figure.inline-fig img{display:block;width:100%;height:auto;cursor:zoom-in;background:#f3f6f7}
.reader figure.inline-fig figcaption{font-size:12.5px;color:var(--muted);padding:8px 12px;background:#f4f8f9;border-top:1px solid var(--line);line-height:1.6}
@media (max-width:600px){
  .reader figure.inline-fig{max-width:100%}
}

/* 表格：默认换行，超宽时容器内横向滚动 */
.tbl-wrap{overflow-x:auto;margin:12px 0 18px;border:1px solid var(--line);border-radius:10px}
.reader table{border-collapse:collapse;width:100%;margin:0;font-size:13.5px}
.reader th,.reader td{border-bottom:1px solid var(--line);border-right:1px solid var(--line);
  padding:8px 10px;text-align:left;vertical-align:top;word-break:break-word}
.reader th{background:#eef6f7;font-weight:700;color:var(--ink)}
.reader tr:nth-child(even) td{background:#fafcfc}
.reader td:last-child,.reader th:last-child{border-right:none}
.reader tr:last-child td{border-bottom:none}

.progress-bar{height:6px;background:#e3eaed;border-radius:999px;overflow:hidden;margin:6px 0}
.progress-bar > i{display:block;height:100%;background:linear-gradient(90deg,var(--teal),var(--blue))}

/* quiz */
.q-card .q-meta{font-size:12.5px;color:var(--muted);margin-bottom:8px}
.q-stem{font-size:16.5px;font-weight:600;margin-bottom:14px;white-space:pre-wrap;line-height:1.6}
.opt{display:block;width:100%;text-align:left;border:1px solid var(--line);background:#fff;
  border-radius:10px;padding:13px 14px;margin-bottom:10px;font-size:15px;transition:.12s;line-height:1.5}
.opt:hover{border-color:var(--teal)}
.opt.sel{border-color:var(--teal);background:#eaf6f7}
.opt.correct{border-color:var(--green);background:#e9f7ee}
.opt.wrong{border-color:var(--red);background:#fdecea}
.opt .mk{font-weight:800;margin-right:8px}
.opt .lab{display:inline-block;width:22px;height:22px;line-height:22px;text-align:center;
  border-radius:50%;background:#eef6f7;color:var(--teal-d);font-weight:700;margin-right:8px;font-size:13px}
.explain{background:#f3f8f9;border-left:3px solid var(--teal);padding:11px 13px;border-radius:6px;
  font-size:14px;color:#37464c;margin-top:8px;line-height:1.7}
.q-nav{display:flex;gap:10px;margin-top:16px}

/* result */
.stat-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(120px,1fr));gap:12px;margin:14px 0}
.stat{background:#f6fafb;border:1px solid var(--line);border-radius:10px;padding:14px;text-align:center}
.stat b{display:block;font-size:26px;color:var(--teal-d)}
.stat span{font-size:12px;color:var(--muted)}

/* lists */
.list-item{display:flex;gap:10px;align-items:center;padding:12px;border:1px solid var(--line);
  border-radius:10px;margin-bottom:10px;background:#fff}
.list-item .li-main{flex:1;min-width:0}
.list-item .li-title{font-weight:600;font-size:14.5px;line-height:1.5}
.list-item .li-sub{font-size:12px;color:var(--muted)}
.list-item .iconbtn{white-space:nowrap}

/* toast */
.toast{position:fixed;left:50%;bottom:80px;transform:translateX(-50%) translateY(20px);
  background:#263238;color:#fff;padding:10px 18px;border-radius:999px;font-size:14px;opacity:0;
  pointer-events:none;transition:.25s;z-index:60;max-width:90vw;text-align:center}
.toast.show{opacity:1;transform:translateX(-50%) translateY(0)}
.tag-ok{color:var(--green);font-weight:700}
.tag-bad{color:var(--red);font-weight:700}
.banner{background:#fff8ef;border:1px solid #ffe2c2;color:#9a5b12;border-radius:10px;
  padding:10px 12px;font-size:13px;margin-bottom:14px;line-height:1.6}

@media (max-width:760px){
  body{font-size:16px}
  .topnav{display:none}
  .view{padding:12px;padding-bottom:78px}
  .tabbar{display:flex;position:fixed;left:0;right:0;bottom:0;z-index:40;
    background:#fff;border-top:1px solid var(--line);
    padding:6px 0 calc(6px + env(safe-area-inset-bottom));justify-content:space-around}
  .tabbar a{display:flex;flex-direction:column;align-items:center;gap:2px;font-size:11px;color:var(--muted);flex:1}
  .tabbar a span{font-size:18px}
  .tabbar a.active{color:var(--teal)}
  .study{grid-template-columns:1fr}
  .tree{position:fixed;left:0;right:0;bottom:54px;top:auto;max-height:62vh;background:#fff;
    border-top:1px solid var(--line);padding:10px;transform:translateY(110%);transition:.25s;z-index:35;
    box-shadow:0 -6px 20px rgba(0,0,0,.12)}
  .tree.open{transform:translateY(0)}
  .reader{padding:18px 16px;border-radius:12px}
  .reader h2.sec-title{font-size:20px}
  .reader p{font-size:16px;line-height:1.85}
  .reader h3.sub{font-size:16.5px}
  .brand-text small{display:none}
  .subj-tab{padding:5px 9px;font-size:12px}
  .opt{font-size:15.5px;padding:14px}
}
.tree-toggle{display:none}
@media (max-width:760px){.tree-toggle{display:inline-block;margin-bottom:10px}}