:root{
  --primary:#1a6fb5; --primary-d:#134e80; --green:#2e8b57; --amber:#c07a00;
  --bg:#f4f7fa; --card:#ffffff; --line:#e2e8ef; --text:#1f2d3a; --muted:#6b7c8d;
}
*{box-sizing:border-box}
body{margin:0;font-family:-apple-system,"PingFang SC","Microsoft YaHei",Segoe UI,sans-serif;background:var(--bg);color:var(--text);font-size:15px}
.hidden{display:none!important}
.sub{color:var(--muted);font-size:13px}
a{color:var(--primary)}

/* buttons */
.btn{border:1px solid var(--line);background:#fff;color:var(--text);padding:9px 16px;border-radius:8px;cursor:pointer;font-size:14px}
.btn.primary{background:var(--primary);border-color:var(--primary);color:#fff}
.btn.ghost{background:#fff}
.btn.danger{background:#fff;color:#a32d2d;border-color:#e3b3b3}
.btn.sm{padding:6px 12px;font-size:13px}
.btn.block{width:100%;margin-top:8px}
.btn:hover{filter:brightness(.97)}

/* auth */
.auth-view{display:flex;align-items:center;justify-content:center;min-height:100vh;padding:20px}
.auth-card{background:var(--card);border:1px solid var(--line);border-radius:14px;padding:28px;width:100%;max-width:360px;box-shadow:0 8px 30px rgba(20,50,80,.08)}
.auth-card h1{margin:0 0 4px;font-size:22px;color:var(--primary-d)}
.auth-card .sub{margin:0 0 18px}
.tabs{display:flex;gap:8px;margin-bottom:16px}
.tab{flex:1;padding:10px;border:1px solid var(--line);background:#fff;border-radius:8px;cursor:pointer;color:var(--muted)}
.tab.active{background:var(--primary);color:#fff;border-color:var(--primary)}
#login-form input,#register-form input,#pwd-form input{width:100%;padding:11px 12px;margin-bottom:12px;border:1px solid var(--line);border-radius:8px;font-size:15px}
.hint{font-size:13px;min-height:18px;margin-top:4px}
.hint.ok{color:var(--green)} .hint.err{color:#a32d2d}

/* topbar */
.topbar{display:flex;align-items:center;gap:10px;padding:10px 16px;background:var(--primary-d);color:#fff}
.brand{font-weight:600;font-size:16px}
.spacer{flex:1}
.user-info{font-size:13px;opacity:.95}
.nav-toggle{display:none;background:transparent;border:none;color:#fff;font-size:22px;cursor:pointer}

/* nav */
.main-nav{display:flex;gap:6px;padding:8px 16px;background:var(--card);border-bottom:1px solid var(--line);flex-wrap:wrap}
.nav-btn{padding:9px 16px;border:none;background:transparent;color:var(--muted);border-radius:8px;cursor:pointer;font-size:14px}
.nav-btn.active{background:var(--primary);color:#fff}
.content{padding:18px;max-width:1100px;margin:0 auto}

/* doc meta + progress */
.doc-meta{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:14px;margin-bottom:14px;font-size:13px;line-height:1.7}
.study-progress{display:flex;align-items:center;gap:12px;margin-bottom:14px}
.study-progress .bar{flex:1;height:10px;background:#e8eef4;border-radius:6px;overflow:hidden}
.bar-fill{height:100%;width:0;background:var(--green);transition:width .3s}
#study-progress-text{font-size:13px;color:var(--muted);white-space:nowrap}

/* study layout */
.layout-2{display:grid;grid-template-columns:300px 1fr;gap:16px}
.doc-list{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:8px;max-height:76vh;overflow:auto}
.doc-chapter{margin-bottom:4px}
.doc-ch-head{padding:10px 12px;font-weight:600;font-size:13px;cursor:pointer;background:#f0f5fa;border-radius:8px}
.doc-ch-body{max-height:0;overflow:hidden;transition:max-height .25s}
.doc-ch-body.open{max-height:600px;overflow:auto}
.doc-item{display:flex;justify-content:space-between;align-items:center;padding:8px 12px;border-radius:6px;cursor:pointer;font-size:13px}
.doc-item:hover{background:#f0f4f8}
.doc-item.read{color:var(--green)}
.badge{font-size:11px;padding:2px 7px;border-radius:10px;background:#eef2f6;color:var(--muted)}
.badge.read{background:#e3f3e0;color:var(--green)}
.doc-reader{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:22px;max-height:76vh;overflow:auto}
.doc-reader h2{color:var(--primary-d);margin:0 0 6px}
.doc-reader .meta{color:var(--muted);font-size:12px;margin-bottom:14px}
.doc-text{font-size:14.5px;line-height:1.95;white-space:pre-wrap}
.doc-toolbar{margin-top:16px}
.placeholder{color:var(--muted);text-align:center;margin-top:60px}

/* exam */
.q-card{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:18px;margin-bottom:14px}
.q-head{display:flex;gap:10px;align-items:baseline;margin-bottom:10px;flex-wrap:wrap}
.q-type{font-size:11px;padding:2px 8px;border-radius:8px;background:#eef2f6;color:var(--muted)}
.q-src{font-size:12px;color:var(--primary);background:#eef5fb;padding:3px 8px;border-radius:6px}
.q-text{font-size:14.5px;margin-bottom:12px}
.blank{display:inline-block;min-width:60px;border-bottom:2px solid var(--primary);color:var(--primary-d);font-weight:600;padding:0 4px}
.opt{display:block;padding:10px 12px;border:1px solid var(--line);border-radius:8px;margin-bottom:8px;cursor:pointer;font-size:14px}
.opt:hover{background:#f0f4f8}
.opt.correct{background:#e3f3e0;border-color:var(--green)}
.opt.wrong{background:#fcebeb;border-color:#a32d2d}
.opt input{margin-right:8px}
.fill-input{width:220px;max-width:100%;padding:8px 10px;border:1px solid var(--line);border-radius:8px}

/* result */
.result-banner{font-size:20px;font-weight:700;text-align:center;padding:18px;border-radius:12px;margin-bottom:14px}
.result-banner.pass{background:#e3f3e0;color:var(--green)}
.result-banner.fail{background:#fcebeb;color:#a32d2d}
.result-box{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:22px;text-align:center}

/* scores / wrong */
#scores-list table,#admin-users table{width:100%;border-collapse:collapse;margin-top:8px;background:var(--card);font-size:13.5px}
th,td{border:1px solid var(--line);padding:9px 10px;text-align:left}
th{background:#f0f5fa;color:var(--muted)}
.tag{font-size:11px;padding:2px 8px;border-radius:10px}
.tag.ok{background:#e3f3e0;color:var(--green)}
.tag.pending{background:#fdf0d9;color:var(--amber)}
.wrong-item{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:14px;margin-bottom:10px}
.wrong-item .q-text{font-size:14px;margin:6px 0}
.wrong-item .q-ans{font-size:13px;color:var(--green)}

/* admin */
.stat-cards{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;margin:10px 0}
.stat{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:16px;text-align:center}
.stat .num{font-size:26px;font-weight:700;color:var(--primary)}
.stat .lbl{font-size:12px;color:var(--muted);margin-top:4px}

/* modal */
.modal{position:fixed;inset:0;background:rgba(0,0,0,.4);display:flex;align-items:center;justify-content:center;padding:20px;z-index:50}
.modal-card{background:#fff;border-radius:12px;padding:24px;width:100%;max-width:340px}
.modal-card h3{margin:0 0 12px}

/* table scroll for small screens */
.table-scroll{overflow-x:auto}

/* ---------- responsive (mobile) ---------- */
@media (max-width:720px){
  body{font-size:14px}
  .nav-toggle{display:block}
  .main-nav{flex-direction:column;display:none;padding:8px}
  .main-nav.open{display:flex}
  .nav-btn{width:100%;text-align:left}
  .content{padding:12px}
  .layout-2{grid-template-columns:1fr}
  .doc-list{max-height:none}
  .doc-ch-body.open{max-height:none}
  .doc-reader{max-height:none}
  .stat-cards{grid-template-columns:repeat(2,1fr)}
  .brand{font-size:14px}
  .user-info{font-size:12px}
  .btn,#login-form input,#register-form input,#pwd-form input,.opt,.fill-input{font-size:16px}
  .opt,.btn,.nav-btn,.doc-item,.doc-ch-head{min-height:44px}
  th,td{padding:8px 6px;font-size:12.5px}
}