* { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --bg: #f5f7fa; --card: #ffffff; --line: #e4e8ef;
  --ink: #1f2937; --muted: #6b7280; --blue: #2c6fbb; --blue-d: #1f4e79;
  --green: #1e7546; --red: #b3261e; --amber: #e0862e;
}
body { font-family: -apple-system, "Segoe UI", "Microsoft YaHei", sans-serif; color: var(--ink); font-size: 15px; line-height: 1.6;
  background: radial-gradient(circle at 12% 16%, rgba(44,111,187,.10), transparent 42%), radial-gradient(circle at 88% 10%, rgba(16,185,129,.10), transparent 40%), radial-gradient(circle at 50% 96%, rgba(99,102,241,.09), transparent 46%), linear-gradient(160deg, #e3edfb 0%, #f4f8fe 45%, #eaf6ee 100%);
  background-attachment: fixed; }
a { color: var(--blue); }

.topbar { background: linear-gradient(120deg,#1f4e79 0%,#2c6fbb 55%,#3b82d9 100%); color: #fff; padding: 14px 22px; display: flex; align-items: center; justify-content: space-between; position: sticky; top: 0; z-index: 10; box-shadow: 0 4px 16px rgba(31,78,121,.25); }
.topbar .brand { font-size: 18px; font-weight: 700; }
.topbar .meta { font-size: 14px; opacity: .95; }
.topbar a, .topbar button { color: #fff; background: rgba(255,255,255,.15); border: none; padding: 6px 14px; border-radius: 6px; cursor: pointer; font-size: 14px; text-decoration: none; margin-left: 10px; }
.topbar button:hover { background: rgba(255,255,255,.28); }

.container { max-width: 860px; margin: 24px auto; padding: 0 16px; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 24px; margin-bottom: 18px; box-shadow: 0 1px 3px rgba(0,0,0,.04); }

.auth-wrap { max-width: 400px; margin: 60px auto; }
.auth-wrap h1 { font-size: 22px; margin-bottom: 6px; color: var(--blue-d); }
.auth-wrap .sub { color: var(--muted); margin-bottom: 22px; }
label { display: block; margin: 12px 0 4px; font-weight: 600; }
input[type=text], input[type=password] { width: 100%; padding: 10px 12px; border: 1px solid var(--line); border-radius: 8px; font-size: 15px; }
input:focus { outline: 2px solid var(--blue); border-color: transparent; }

/* ===== 键盘焦点可见（2026-09 无障碍修复）===== */
:focus-visible{outline:2.5px solid #2c6fbb;outline-offset:2px;}
.topbar :focus-visible,.hd :focus-visible{outline-color:#fff;outline-offset:1px;}

.btn { display: inline-block; width: 100%; padding: 11px; background: var(--blue); color: #fff; border: none; border-radius: 8px; font-size: 16px; cursor: pointer; margin-top: 18px; font-weight: 600; }
.btn:hover { background: var(--blue-d); }
.btn.ghost { background: transparent; color: var(--blue); border: 1px solid var(--blue); }
.msg { margin-top: 12px; font-size: 14px; min-height: 20px; }
.msg.err { color: var(--red); } .msg.ok { color: var(--green); }

.tabs { display: flex; gap: 8px; margin-bottom: 16px; }
.tabs button { flex: 1; padding: 9px; border: 1px solid var(--line); background: #fff; border-radius: 8px; cursor: pointer; font-size: 14px; }
.tabs button.on { background: var(--blue); color: #fff; border-color: var(--blue); }
.small { font-size: 13px; color: var(--muted); }

/* 题目 */
.qtag { display: inline-block; font-size: 12px; color: #fff; background: var(--blue); border-radius: 4px; padding: 1px 8px; margin-right: 8px; vertical-align: middle; }
.qtitle { font-size: 16px; font-weight: 600; }
.qbody pre { background: #f6f8fa; border: 1px solid var(--line); border-radius: 8px; padding: 12px 14px; overflow-x: auto; font-family: Consolas, "Courier New", monospace; font-size: 13.5px; line-height: 1.5; margin: 10px 0; white-space: pre; }
.qbody p { margin: 8px 0; }
.opts { margin-top: 10px; }
.opt { display: flex; align-items: flex-start; gap: 10px; padding: 8px 12px; border: 1px solid var(--line); border-radius: 8px; margin-bottom: 8px; cursor: pointer; transition: .12s; }
.opt:hover { border-color: var(--blue); background: #f0f6fc; }
.opt.selected { border-color: var(--blue); background: #e8f1fb; }
.opt .k { font-weight: 700; color: var(--blue-d); min-width: 22px; }
.opt.correct-ans { border-color: var(--green); background: #eaf6ef; }
.opt.wrong-ans { border-color: var(--red); background: #fdeeee; }
.opt input { margin-top: 4px; }

.progress { display: flex; align-items: center; gap: 12px; }
.progress .bar { flex: 1; height: 8px; background: rgba(255,255,255,.25); border-radius: 4px; overflow: hidden; }
.progress .bar > i { display: block; height: 100%; background: #7fd0a0; }

/* 教师端 */
table { width: 100%; border-collapse: collapse; font-size: 14px; }
th, td { text-align: left; padding: 10px 12px; border-bottom: 1px solid var(--line); }
th { background: #f0f4f9; font-weight: 600; }
tr.clickable { cursor: pointer; }
tr.clickable:hover { background: #f0f6fc; }
.pill { display: inline-block; padding: 2px 10px; border-radius: 12px; font-size: 13px; font-weight: 600; }
.pill.good { background: #eaf6ef; color: var(--green); } .pill.bad { background: #fdeeee; color: var(--red); }
.stat-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); gap: 12px; margin-bottom: 18px; }
.stat { background: #fff; border: 1px solid var(--line); border-radius: 10px; padding: 14px; }
.stat .n { font-size: 26px; font-weight: 700; color: var(--blue-d); }
.stat .l { font-size: 13px; color: var(--muted); }
.detail-item { border: 1px solid var(--line); border-radius: 8px; padding: 10px 14px; margin-bottom: 8px; }
.detail-item .dtitle { font-weight: 600; }
.detail-item .row { font-size: 13.5px; color: var(--muted); margin-top: 4px; }
.rate-low { color: var(--red); font-weight: 700; }
.muted { color: var(--muted); }
.flex { display: flex; gap: 12px; align-items: center; flex-wrap: wrap; }
.spacer { flex: 1; }
h2 { font-size: 19px; color: var(--blue-d); margin-bottom: 14px; }

/* ===== 移动端通用优化（2026-09 新增）===== */
@media(max-width:768px){
  html,body{overflow-x:hidden;}
  table{display:block;max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch;}
  button,.btn{min-height:36px;}
  input,select,textarea{font-size:16px;}
  .modal{padding:12px;}
}