:root{
  --bg:#f6f7fb;
  --card:#ffffff;
  --text:#111827;
  --muted:#6b7280;
  --border:#e5e7eb;
  --primary:#2563eb;
  --primary-weak:#eef2ff;
  --danger:#dc2626;
  --danger-weak:#fef2f2;
  --ok:#16a34a;
  --ok-weak:#ecfdf5;
  --shadow: 0 10px 30px rgba(17,24,39,.06);
  --radius:16px;
}

*{box-sizing:border-box}
body{
  font-family: system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,
    "PingFang SC","Noto Sans CJK SC","Microsoft YaHei",sans-serif;
  background: var(--bg);
  margin:0;
  color: var(--text);
  line-height:1.6;
}

/* 容器：电脑不超宽，手机边距合理 */
.container{
  max-width: 980px;
  margin: 0 auto;
  padding: 18px 14px;
}
@media(min-width:768px){
  .container{padding: 28px 22px;}
}

/* 顶部导航更像“条” */
nav{
  display:flex;
  gap:10px;
  flex-wrap:wrap;
  align-items:center;
  padding: 10px 12px;
  border:1px solid var(--border);
  background: rgba(255,255,255,.7);
  backdrop-filter: blur(8px);
  border-radius: 14px;
  margin-bottom: 14px;
}
nav a{
  display:inline-flex;
  align-items:center;
  gap:6px;
  padding:8px 10px;
  border-radius: 12px;
  border:1px solid transparent;
  color:#1f2937;
}
nav a:hover{
  background:#fff;
  border-color: var(--border);
  text-decoration:none;
}

/* 卡片 */
.card{
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
  box-shadow: var(--shadow);
  margin-bottom: 14px;
}
@media(min-width:768px){
  .card{padding: 22px;}
}

a{color: var(--primary); text-decoration:none}
a:hover{text-decoration:underline}

h1,h2,h3{margin:0 0 10px 0; letter-spacing:-.02em}
.small{font-size:12px;color:var(--muted)}

/* 徽章 */
.badge{
  display:inline-flex;
  align-items:center;
  padding: 3px 10px;
  border-radius: 999px;
  background: var(--primary-weak);
  color: #1e40af;
  font-size:12px;
  border:1px solid #dbeafe;
  margin-left:6px;
}

/* KPI */
.kpi{display:flex;justify-content:space-between;align-items:flex-end;gap:12px;flex-wrap:wrap}
.kpi .num{font-size:32px;font-weight:800;letter-spacing:-.03em}

/* 表单 */
form{display:block}
label{display:block; margin: 10px 0 6px 0; color:#111827; font-weight:600; font-size:13px}
input[type=text],input[type=password],select,textarea{
  width:100%;
  padding: 12px 12px;
  border:1px solid var(--border);
  border-radius: 14px;
  background:#fff;
  color: var(--text);
  outline:none;
  transition: box-shadow .15s ease, border-color .15s ease, transform .15s ease;
}
input[type=text]:focus,input[type=password]:focus,select:focus,textarea:focus{
  border-color: #93c5fd;
  box-shadow: 0 0 0 4px rgba(37,99,235,.12);
}

/* 按钮 */
button{
  padding: 11px 14px;
  border-radius: 14px;
  border:1px solid transparent;
  background: var(--primary);
  color:#fff;
  cursor:pointer;
  font-weight:700;
  transition: transform .06s ease, filter .15s ease, box-shadow .15s ease;
  box-shadow: 0 10px 18px rgba(37,99,235,.18);
}
button:hover{filter:brightness(.98)}
button:active{transform: translateY(1px)}
button.secondary{
  background:#111827;
  box-shadow: 0 10px 18px rgba(17,24,39,.14);
}
button.danger{
  background: var(--danger);
  box-shadow: 0 10px 18px rgba(220,38,38,.16);
}

/* grid */
.grid{display:grid;gap:12px}
.grid.two{grid-template-columns:repeat(2,minmax(0,1fr))}
@media(max-width:820px){.grid.two{grid-template-columns:1fr}}

/* 题目区（更像练习App） */
.question-meta{
  display:flex;
  gap:10px;
  align-items:center;
  flex-wrap:wrap;
  margin-top: 6px;
}
.question-stem{
  margin-top: 12px;
  font-size: 18px;
  line-height: 1.75;
}
@media(max-width:480px){
  .question-stem{font-size:17px}
}

/* ✅ 选项卡片：radio/checkbox 隐藏，整块可点 */
.choice{
  display:flex;
  align-items:flex-start;
  gap:12px;
  padding: 12px 12px;
  border: 1px solid var(--border);
  border-radius: 16px;
  background: #fff;
  margin: 10px 0;
  cursor:pointer;
  transition: border-color .15s ease, box-shadow .15s ease, transform .06s ease, background .15s ease;
  position:relative;
}
.choice:hover{
  border-color:#c7d2fe;
  box-shadow: 0 10px 22px rgba(99,102,241,.10);
}
.choice:active{transform: translateY(1px)}
.choice strong{
  font-weight:800;
  color:#111827;
}
.choice .opt-text{
  flex:1;
  color:#111827;
}
.choice input{
  /* 隐藏原生控件，但保留可访问性 */
  position:absolute;
  opacity:0;
  pointer-events:none;
}

/* 左侧圆点/方块指示器 */
.choice::before{
  content:"";
  width:18px;
  height:18px;
  border-radius: 999px;
  border:2px solid #cbd5e1;
  margin-top: 2px;
  flex:0 0 18px;
  background:#fff;
}
.choice.multi::before{
  border-radius:6px;
}

/* 选中态：需要配合 HTML 结构（见下方小改动） */
.choice.is-selected{
  border-color:#93c5fd;
  background: #f8fbff;
  box-shadow: 0 10px 22px rgba(37,99,235,.12);
}
.choice.is-selected::before{
  border-color: var(--primary);
  background: var(--primary);
  box-shadow: 0 0 0 4px rgba(37,99,235,.12);
}

/* 正确/错误提示块 */
.ok{
  background: var(--ok-weak);
  border:1px solid #bbf7d0;
  color:#166534;
  padding:12px;
  border-radius: 16px;
}
.err{
  background: var(--danger-weak);
  border:1px solid #fecaca;
  color:#991b1b;
  padding:12px;
  border-radius: 16px;
}
.alert{
  background:#fffbeb;
  border:1px solid #fde68a;
  color:#92400e;
  padding:12px;
  border-radius: 16px;
}

hr{border:0;border-top:1px solid var(--border);margin:14px 0}
.footer{margin-top:22px;color:var(--muted);font-size:12px}