/* ===== 数学乐园 · 四年级 ===== */
:root {
  --c-primary: #ff9f43;
  --c-primary-dark: #f57c00;
  --c-blue: #4a90d9;
  --c-green: #2ecc71;
  --c-red: #e74c3c;
  --c-bg: #fff8ef;
  --c-card: #ffffff;
  --c-text: #2d3436;
  --c-text-light: #636e72;
  --c-border: #ffe0b2;
  --radius: 16px;
  --shadow: 0 2px 10px rgba(0, 0, 0, 0.06);
}

* { box-sizing: border-box; margin: 0; padding: 0; }

html { -webkit-text-size-adjust: 100%; }

body {
  font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans CJK SC", sans-serif;
  background: var(--c-bg);
  color: var(--c-text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  font-size: 16px;
  line-height: 1.6;
}

/* ===== 顶栏 ===== */
.topbar {
  background: linear-gradient(120deg, #ff9f43, #ff7e5f);
  color: #fff;
  padding: 10px 16px;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 10px;
  box-shadow: 0 2px 8px rgba(245, 124, 0, 0.3);
  position: sticky;
  top: 0;
  z-index: 10;
}
.brand { font-size: 22px; font-weight: 800; letter-spacing: 1px; }
.brand-sub {
  font-size: 13px; font-weight: 600; background: rgba(255,255,255,0.25);
  padding: 2px 8px; border-radius: 999px; margin-left: 6px; vertical-align: 3px;
}
.nav { display: flex; gap: 6px; flex-wrap: wrap; margin-left: 8px; }
.nav-btn {
  border: none; background: rgba(255,255,255,0.18); color: #fff;
  padding: 8px 14px; border-radius: 999px; font-size: 15px; font-weight: 600;
  cursor: pointer; transition: background 0.15s;
}
.nav-btn:hover { background: rgba(255,255,255,0.32); }
.nav-btn.active { background: #fff; color: var(--c-primary-dark); }
.tools { margin-left: auto; display: flex; gap: 8px; }
.tool-btn {
  border: none; background: rgba(255,255,255,0.2); color: #fff;
  padding: 8px 12px; border-radius: 10px; font-size: 13px; cursor: pointer;
}
.tool-btn:hover { background: rgba(255,255,255,0.35); }

/* ===== 主体 ===== */
.main { flex: 1; width: 100%; max-width: 960px; margin: 0 auto; padding: 20px 16px 40px; }

.foot {
  text-align: center; color: var(--c-text-light); font-size: 12.5px;
  padding: 14px; border-top: 1px solid var(--c-border);
}
.foot a { color: var(--c-primary-dark); }

/* ===== 卡片 ===== */
.card {
  background: var(--c-card); border-radius: var(--radius); box-shadow: var(--shadow);
  padding: 20px; margin-bottom: 16px; border: 1px solid #fff3e0;
}
.card h2 { font-size: 20px; margin-bottom: 10px; color: var(--c-primary-dark); }
.card h3 { font-size: 17px; margin: 14px 0 8px; color: var(--c-text); }

/* ===== 首页 ===== */
.hero {
  text-align: center; padding: 34px 20px; background: linear-gradient(135deg, #fff3e0, #ffe8cc);
  border-radius: var(--radius); margin-bottom: 18px;
}
.hero h1 { font-size: 30px; color: var(--c-primary-dark); margin-bottom: 6px; }
.hero p { color: var(--c-text-light); }
.grid3 { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 14px; }
.menu-card {
  background: var(--c-card); border-radius: var(--radius); box-shadow: var(--shadow);
  padding: 22px; text-align: center; cursor: pointer; border: 1px solid #fff3e0;
  transition: transform 0.12s, box-shadow 0.12s;
}
.menu-card:hover { transform: translateY(-3px); box-shadow: 0 6px 16px rgba(0,0,0,0.1); }
.menu-card .icon { font-size: 40px; }
.menu-card .name { font-size: 19px; font-weight: 700; margin: 8px 0 4px; }
.menu-card .desc { font-size: 13.5px; color: var(--c-text-light); }
.stat-row { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 18px; }
.stat-box {
  flex: 1; min-width: 130px; background: #fff; border-radius: 12px; padding: 14px;
  text-align: center; box-shadow: var(--shadow); border: 1px solid #fff3e0;
}
.stat-box .num { font-size: 26px; font-weight: 800; color: var(--c-primary-dark); }
.stat-box .label { font-size: 13px; color: var(--c-text-light); }

/* ===== 知识库 ===== */
.unit-card { margin-bottom: 16px; }
.unit-head {
  display: flex; align-items: center; gap: 10px; cursor: pointer;
  background: #fff; border-radius: 12px; padding: 12px 16px; box-shadow: var(--shadow);
  border: 1px solid #fff3e0;
}
.unit-head .u-icon { font-size: 26px; }
.unit-head .u-title { font-size: 17px; font-weight: 700; flex: 1; }
.unit-head .u-tag { font-size: 12px; color: var(--c-text-light); }
.unit-head .u-arrow { color: var(--c-text-light); transition: transform 0.15s; }
.unit-head.open .u-arrow { transform: rotate(90deg); }
.unit-body { display: none; padding: 14px 18px; }
.unit-body.open { display: block; }
.kp {
  background: #fffdf7; border-left: 4px solid var(--c-primary); border-radius: 8px;
  padding: 12px 14px; margin: 10px 0;
}
.kp .kp-title { font-weight: 700; margin-bottom: 4px; }
.kp .kp-body { color: var(--c-text); }
.example { background: #f0f7ff; border-left: 4px solid var(--c-blue); border-radius: 8px; padding: 10px 14px; margin: 8px 0; font-size: 15px; }
.example .ex-label { font-weight: 700; color: var(--c-blue); }
.warn { background: #fff0f0; border-left: 4px solid var(--c-red); border-radius: 8px; padding: 10px 14px; margin: 8px 0; font-size: 15px; }
.warn .w-label { font-weight: 700; color: var(--c-red); }
.mastery-btn {
  border: 2px solid var(--c-green); background: #fff; color: var(--c-green);
  border-radius: 999px; padding: 6px 14px; font-size: 13.5px; font-weight: 600; cursor: pointer;
}
.mastery-btn.done { background: var(--c-green); color: #fff; }

/* ===== 练习 ===== */
.panel-row { display: flex; flex-wrap: wrap; gap: 16px; align-items: center; margin-bottom: 12px; }
.panel-row label { font-size: 14px; color: var(--c-text-light); }
.chip {
  border: 2px solid var(--c-border); background: #fff; color: var(--c-text);
  border-radius: 999px; padding: 6px 14px; font-size: 14px; font-weight: 600; cursor: pointer;
}
.chip.on { border-color: var(--c-primary); background: var(--c-primary); color: #fff; }
select, input[type="number"], input[type="text"] {
  font-size: 16px; padding: 8px 12px; border-radius: 10px; border: 2px solid var(--c-border);
  outline: none; font-family: inherit;
}
select:focus, input:focus { border-color: var(--c-primary); }
.btn {
  border: none; border-radius: 12px; padding: 10px 22px; font-size: 16px; font-weight: 700;
  cursor: pointer; transition: filter 0.12s;
}
.btn-primary { background: var(--c-primary); color: #fff; }
.btn-green { background: var(--c-green); color: #fff; }
.btn-blue { background: var(--c-blue); color: #fff; }
.btn-ghost { background: #eee; color: var(--c-text); }
.btn:hover { filter: brightness(1.05); }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }

/* 题目 */
.q-card { margin-bottom: 14px; }
.q-prompt { font-size: 21px; font-weight: 700; padding: 6px 0 10px; }
.q-math { font-family: "Courier New", ui-monospace, monospace; }
.q-answer { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.q-answer input { width: 150px; }
.q-result { margin-top: 10px; padding: 10px 14px; border-radius: 10px; font-size: 15px; display: none; }
.q-result.right { background: #e8f8ee; color: #0b7a3b; display: block; }
.q-result.wrong { background: #fdecea; color: #a8231a; display: block; }
.q-result .sol { margin-top: 6px; color: var(--c-text); }
.q-tag { font-size: 12px; background: #eee; border-radius: 6px; padding: 2px 8px; color: var(--c-text-light); }
.q-vertical { font-family: "Courier New", ui-monospace, monospace; font-size: 19px; line-height: 1.35; white-space: pre; margin: 6px 0; }

/* 本轮小结 */
.summary-big { text-align: center; font-size: 22px; font-weight: 800; margin: 8px 0; }
.progress-bar { height: 12px; background: #f1f2f6; border-radius: 999px; overflow: hidden; margin: 10px 0; }
.progress-bar > div { height: 100%; background: linear-gradient(90deg, var(--c-green), #27ae60); border-radius: 999px; transition: width 0.3s; }

/* ===== 错题本 ===== */
.err-item { border: 1px solid #ffd6d6; border-left: 4px solid var(--c-red); }
.err-item.done { border-left-color: var(--c-green); opacity: 0.75; }
.err-q { font-size: 18px; font-weight: 700; }
.err-meta { font-size: 13px; color: var(--c-text-light); margin-top: 6px; display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }
.reason-btns { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 8px; }
.reason-btn { border: 1.5px solid var(--c-border); background: #fff; border-radius: 999px; padding: 3px 10px; font-size: 12.5px; cursor: pointer; }
.reason-btn.on { border-color: var(--c-primary); background: var(--c-primary); color: #fff; }
.empty-tip { text-align: center; color: var(--c-text-light); padding: 30px; font-size: 15px; }
.badge { display: inline-block; font-size: 12px; border-radius: 999px; padding: 2px 10px; font-weight: 600; }
.badge.red { background: #fdecea; color: #a8231a; }
.badge.green { background: #e8f8ee; color: #0b7a3b; }

/* ===== 小工具 ===== */
.row { display: flex; gap: 10px; flex-wrap: wrap; }
.mt10 { margin-top: 10px; }
.mt20 { margin-top: 20px; }
.muted { color: var(--c-text-light); font-size: 13px; }
.center { text-align: center; }
@media (max-width: 640px) {
  body { font-size: 15px; }
  .brand { font-size: 18px; }
  .hero h1 { font-size: 24px; }
  .tools .tool-btn { font-size: 12px; padding: 6px 8px; }
  .q-prompt { font-size: 18px; }
}