:root{
  --bg:#f5f6f8; --card:#fff; --ink:#1f2329; --muted:#8a94a6;
  --line:#e6e8ec; --brand:#2f6df6; --brand-d:#1f54d6; --accent:#eef3ff;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  background:var(--bg); color:var(--ink);
  font:16px/1.7 -apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;
}
a{color:var(--brand);text-decoration:none}
a:hover{text-decoration:underline}

.topbar{
  display:flex;align-items:center;gap:16px;
  background:#fff;border-bottom:1px solid var(--line);
  padding:12px 20px;position:sticky;top:0;z-index:10;
}
.brand{font-size:20px;font-weight:700;color:var(--ink)}
.brand span{color:var(--muted);font-weight:400;font-size:14px}
.search{margin-left:auto;display:flex;gap:6px}
.search input{
  width:240px;max-width:46vw;padding:8px 12px;border:1px solid var(--line);
  border-radius:8px;font-size:14px;outline:none}
.search input:focus{border-color:var(--brand)}
.search button{
  padding:8px 16px;border:0;border-radius:8px;background:var(--brand);color:#fff;
  cursor:pointer;font-size:14px}
.search button:hover{background:var(--brand-d)}
.userbox{display:flex;align-items:center;gap:14px;white-space:nowrap}
.userbox .hello{color:var(--muted);font-size:14px}
.userbox .nav-link{font-size:14px;color:var(--brand-d);font-weight:600}

.container{max-width:920px;margin:24px auto;padding:0 16px}

/* flash messages */
.flash{padding:10px 14px;border-radius:8px;margin-bottom:16px;font-size:14px}
.flash.ok{background:#e7f6ec;border:1px solid #9dd6ad;color:#2e8b57}
.flash.err{background:#fdecec;border:1px solid #f0b4b4;color:#c0392b}

/* login page */
.login-body{display:flex;align-items:center;justify-content:center;min-height:100vh;background:var(--bg)}
.login-card{
  background:#fff;border:1px solid var(--line);border-radius:14px;
  padding:32px 30px;width:320px;max-width:90vw;box-shadow:0 8px 30px rgba(0,0,0,.06)}
.login-title{margin:0 0 18px;font-size:22px;text-align:center;color:var(--ink)}
.login-card form{display:flex;flex-direction:column;gap:14px}
.login-card label{display:flex;flex-direction:column;gap:6px;font-size:14px;color:var(--muted)}
.login-card input{padding:10px 12px;border:1px solid var(--line);border-radius:8px;font-size:15px;outline:none}
.login-card input:focus{border-color:var(--brand)}
.login-card button{
  margin-top:6px;padding:11px;border:0;border-radius:8px;background:var(--brand);
  color:#fff;font-size:15px;cursor:pointer}
.login-card button:hover{background:var(--brand-d)}
.login-error{background:#fdecec;border:1px solid #f0b4b4;color:#c0392b;
  padding:9px 12px;border-radius:8px;font-size:14px;margin-bottom:14px}

/* admin panel */
.admin-add{display:flex;flex-wrap:wrap;gap:10px;align-items:center}
.admin-add input[type=text]{padding:8px 12px;border:1px solid var(--line);border-radius:8px;font-size:14px}
.admin-add .admin-chk{font-size:14px;color:var(--muted);display:flex;align-items:center;gap:5px}
.admin-add button,.admin-table button{
  padding:7px 14px;border:1px solid var(--line);border-radius:8px;background:#fff;
  color:var(--brand-d);cursor:pointer;font-size:13px}
.admin-add button{background:var(--brand);color:#fff;border-color:var(--brand)}
.admin-add button:hover{background:var(--brand-d)}
.admin-table{width:100%;border-collapse:collapse;font-size:14px}
.admin-table th,.admin-table td{padding:9px 8px;border-bottom:1px solid var(--line);text-align:left;vertical-align:middle}
.admin-table th{color:var(--muted);font-weight:600}
.admin-table tr.self{background:#fafbff}
.admin-table .me{color:var(--brand);font-size:12px}
.admin-table form.inline{display:flex;gap:6px;align-items:center;margin:0}
.admin-table input[type=text]{
  width:140px;padding:6px 9px;border:1px solid var(--line);border-radius:7px;font-size:13px}
.admin-table .state{font-size:13px;color:var(--muted)}
.admin-table button.danger{color:#c0392b;border-color:#f0b4b4}
.admin-table button.danger:hover{background:#fdecec}
.admin-table button:hover{border-color:var(--brand)}
.badge-admin{font-size:12px;color:var(--muted)}
.muted{color:var(--muted)}

.crumbs{color:var(--muted);font-size:14px;margin-bottom:16px}
.crumbs i{color:var(--line);font-style:normal;margin:0 2px}

/* 随机跳题 panel (foldable) */
.random-panel{
  background:var(--card);border:1px solid var(--line);border-radius:12px;
  padding:14px 18px;margin-bottom:26px}
.rj-head{display:flex;align-items:center;gap:12px}
.rj-toggle{
  display:flex;align-items:center;gap:7px;cursor:pointer;user-select:none;
  font-size:16px;font-weight:600;padding-left:10px;border-left:4px solid var(--brand)}
.rj-chev::before{content:"\25B8";color:var(--muted);font-weight:400;font-size:13px}  /* ▸ */
.rj-open:checked ~ .rj-head .rj-chev::before{content:"\25BE"}                          /* ▾ */
.rj-go{
  margin-left:auto;padding:9px 24px;border:0;border-radius:8px;
  background:var(--brand);color:#fff;font-size:15px;cursor:pointer}
.rj-go:hover{background:var(--brand-d)}
.rj-body{margin-top:14px}
.rj-open:not(:checked) ~ .rj-body{display:none}
.rj-row{display:flex;flex-wrap:wrap;align-items:center;gap:10px;margin-bottom:12px}
.rj-row:last-child{margin-bottom:0}
.rj-label{flex:0 0 auto;color:var(--muted);font-size:14px}
.rj-label-2{margin-left:22px}
.rj-srcs{display:flex;flex-wrap:wrap;gap:16px}
.rj-srcs label{display:flex;align-items:center;gap:5px;font-size:14px;cursor:pointer}
.rj-range{display:flex;align-items:center;gap:8px;font-size:14px}
.rj-range select{
  padding:6px 10px;border:1px solid var(--line);border-radius:7px;
  font-size:14px;background:#fff;cursor:pointer}
.rj-range select:focus{border-color:var(--brand);outline:none}
.rj-range span{color:var(--muted)}

/* home */
.source-block{margin-bottom:28px}
.source-block h2{font-size:17px;margin:0 0 12px;padding-left:10px;border-left:4px solid var(--brand)}
.match-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(210px,1fr));gap:12px}
.match-card{
  background:var(--card);border:1px solid var(--line);border-radius:12px;
  padding:14px 16px;display:block;color:var(--ink)}
.match-card:hover{border-color:var(--brand);box-shadow:0 4px 14px rgba(47,109,246,.08);text-decoration:none}
.match-card .name{font-weight:600;font-size:15px}
.match-card .meta{color:var(--muted);font-size:13px;margin-top:4px}

/* year tabs */
.years{display:flex;flex-wrap:wrap;gap:8px;margin:14px 0 22px}
.year-chip{
  padding:6px 12px;border:1px solid var(--line);border-radius:999px;
  background:#fff;font-size:14px;color:var(--ink)}
.year-chip:hover{border-color:var(--brand);text-decoration:none}
.year-chip.active{background:var(--brand);color:#fff;border-color:var(--brand)}
.year-chip .cnt{color:var(--muted);font-size:12px;margin-left:4px}
.year-chip.active .cnt{color:#dce6ff}

/* page title */
h1.page{font-size:22px;margin:6px 0 4px}
.subtitle{color:var(--muted);font-size:14px;margin-bottom:10px}

/* problem + solution cards */
.card{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:20px 22px;margin-bottom:18px}
.card-clickable{cursor:pointer;transition:border-color .15s,box-shadow .15s}
.card-clickable:hover{border-color:var(--brand);box-shadow:0 4px 14px rgba(47,109,246,.08)}
.card h3{margin:0 0 10px;font-size:16px;display:flex;align-items:center;gap:10px;flex-wrap:wrap}
.tag{font-size:12px;font-weight:600;padding:2px 9px;border-radius:999px;background:var(--accent);color:var(--brand-d)}
.tag.official{background:#fff4e5;color:#b9760a}

/* foldable solutions (collapsed by default) */
.sol summary{
  list-style:none;cursor:pointer;user-select:none;
  display:flex;align-items:center;gap:10px;flex-wrap:wrap;
  margin:0;font-size:16px;font-weight:700}
.sol summary::-webkit-details-marker{display:none}
.sol[open] summary{margin-bottom:10px}
.sol-chev::before{content:"\25B8";color:var(--muted);font-size:13px}      /* ▸ */
.sol[open] .sol-chev::before{content:"\25BE"}                             /* ▾ */
.sol summary:hover .sol-chev::before{color:var(--brand)}
.h-right{margin-left:auto;display:flex;align-items:center;gap:8px}
.diff{font-size:12px;color:var(--muted);font-weight:400;white-space:nowrap}
.diff.elegance{color:#5a8f5a}
.copy-btn{
  font-size:12px;line-height:1;padding:5px 12px;border:1px solid var(--line);
  border-radius:999px;background:#fff;color:var(--brand-d);cursor:pointer;
  white-space:nowrap;transition:background .15s,border-color .15s}
.copy-btn:hover{background:var(--accent);border-color:var(--brand)}
.copy-btn.copied{background:#e7f6ec;border-color:#9dd6ad;color:#2e8b57}

.content{font-size:16px;overflow-wrap:break-word}
.content p{margin:0 0 10px}
.content p:last-child{margin-bottom:0}

/* problem labels (topic tags) — translucent chips under the statement */
.labels{display:flex;flex-wrap:wrap;gap:8px;margin-top:16px;padding-top:14px;border-top:1px solid var(--line)}
.label{
  font-size:12.5px;line-height:1;padding:5px 11px;border-radius:999px;
  background:rgba(47,109,246,.10);color:var(--brand-d);border:1px solid rgba(47,109,246,.18);
  text-decoration:none;cursor:pointer;transition:background .15s,border-color .15s}
.label:hover{background:rgba(47,109,246,.18);border-color:rgba(47,109,246,.35);text-decoration:none}
.prob-img{max-width:100%;height:auto;display:block;margin:10px auto;border-radius:6px}
/* display math is scaled to fit its column by JS (fitMath) so no scrollbar is needed */
mjx-container{max-width:100%}
mjx-container[display="true"]{overflow:visible}

.empty{color:var(--muted);font-style:italic}
.notice{background:#fff;border:1px dashed var(--line);border-radius:12px;padding:30px;text-align:center;color:var(--muted)}

/* ---- responsive / mobile ---- */
/* wide tables scroll inside their card instead of overflowing the page */
.table-wrap{overflow-x:auto;-webkit-overflow-scrolling:touch}
.admin-table{min-width:520px}   /* keep columns usable; the wrapper scrolls when narrower */

@media (max-width:640px){
  /* topbar stacks: brand + user links on row 1, full-width search on row 2 */
  .topbar{flex-wrap:wrap;gap:10px;padding:10px 14px}
  .brand{font-size:18px}
  .userbox{margin-left:auto;gap:12px}
  .search{order:3;flex-basis:100%;margin-left:0}
  .search input{flex:1;width:auto;max-width:none}

  /* tighter spacing on small screens */
  .container{margin:16px auto;padding:0 12px}
  .card{padding:16px 14px}
  .random-panel{padding:12px 14px}
  h1.page{font-size:20px}
  .rj-label-2{margin-left:0}

  /* ≥16px form fields so iOS doesn't zoom in on focus */
  .search input,.login-card input,.admin-add input,.admin-table input,.rj-range select{font-size:16px}
}

@media (max-width:380px){
  .userbox .hello{display:none}   /* save the top row; 管理/退出 links remain */
}