* { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --wood: #e3b06d;
  --ink: #2b2b2b;
  --accent: #2e7d5b;
  --accent-dark: #235e45;
  --line: #e2ddd2;
  --bg: #f6f3ec;
}
body {
  font-family: "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.7;
}
button {
  cursor: pointer;
  border: none;
  border-radius: 8px;
  padding: 9px 16px;
  font-size: 15px;
  background: #eceae4;
  transition: .15s;
}
button:hover { filter: brightness(.96); }
button:disabled { opacity: .4; cursor: not-allowed; }
button.primary { background: var(--accent); color: #fff; }
button.primary:hover { background: var(--accent-dark); }

/* ---------- 登录页 ---------- */
.login-page {
  min-height: 100vh;
  display: flex; align-items: center; justify-content: center;
  background: radial-gradient(circle at 30% 20%, #3a4a55, #1d2731);
}
.login-card {
  width: 360px; max-width: 92vw;
  background: #fff; border-radius: 18px; padding: 38px 32px;
  box-shadow: 0 24px 60px rgba(0,0,0,.35); text-align: center;
}
.login-card .logo { font-size: 40px; letter-spacing: -6px; }
.login-card h1 { font-size: 22px; margin: 12px 0 4px; }
.login-card .sub { color: #888; font-size: 14px; margin-bottom: 22px; }
.login-card input {
  width: 100%; padding: 12px 14px; margin-bottom: 12px;
  border: 1px solid var(--line); border-radius: 10px; font-size: 15px;
}
.login-card input:focus { outline: none; border-color: var(--accent); }
.login-card button.primary { width: 100%; padding: 12px; margin-top: 4px; }
.login-card .err { color: #c0392b; font-size: 14px; min-height: 20px; margin-top: 10px; }
.login-card .hint { color: #999; font-size: 12.5px; margin-top: 18px; }
.login-card code { background: #f0eee8; padding: 1px 6px; border-radius: 5px; }

/* ---------- 课程页 ---------- */
.topbar {
  display: flex; justify-content: space-between; align-items: center;
  padding: 12px 22px; background: #fff; border-bottom: 1px solid var(--line);
  position: sticky; top: 0; z-index: 10;
}
.topbar .brand { font-weight: 700; font-size: 17px; }
.topbar .account { display: flex; align-items: center; gap: 12px; font-size: 14px; color: #666; }
.sound-toggle { padding: 7px 10px; white-space: nowrap; }
.sound-toggle.is-muted { color: #888; }

.layout { display: flex; align-items: flex-start; max-width: 1180px; margin: 0 auto; }
.sidebar {
  width: 240px; flex-shrink: 0; padding: 18px 10px;
  position: sticky; top: 56px; align-self: flex-start;
}
.side-title { font-size: 13px; color: #999; padding: 0 12px 8px; }
#lesson-list { list-style: none; }
.lesson-item {
  display: flex; align-items: center; gap: 10px;
  padding: 10px 12px; border-radius: 10px; cursor: pointer; font-size: 15px;
}
.lesson-item:hover { background: #efece5; }
.lesson-item.active { background: var(--accent); color: #fff; }
.lesson-item .num {
  width: 22px; height: 22px; flex-shrink: 0;
  display: flex; align-items: center; justify-content: center;
  background: rgba(0,0,0,.08); border-radius: 50%; font-size: 12px;
}
.lesson-item.active .num { background: rgba(255,255,255,.25); }
.lesson-item .t { flex: 1; }
.lesson-item .check { color: #7bd6a8; font-weight: 700; }
.lesson-item.active .check { color: #d6ffe9; }

.content {
  flex: 1; min-width: 0; padding: 26px 34px 60px;
}
.content h2 { font-size: 24px; margin-bottom: 18px; }
.lesson-text { margin: 0 0 14px; font-size: 16.5px; }
.lesson-text strong { color: var(--accent-dark); }

.diagram { margin: 18px 0; text-align: center; }
.diagram .caption { font-size: 13.5px; color: #888; margin-top: 8px; }

.board-canvas {
  width: 460px; max-width: 100%;
  border-radius: 8px; box-shadow: 0 6px 20px rgba(0,0,0,.18);
}
.board-canvas.small { width: 300px; }

/* 练习区 */
.practice {
  margin: 24px 0; padding: 20px; border: 2px solid var(--accent);
  border-radius: 14px; background: #fbfaf6;
}
.practice-head { font-size: 15.5px; margin-bottom: 14px; }
.practice-head .tag {
  display: inline-block; background: var(--accent); color: #fff;
  font-size: 12px; padding: 2px 9px; border-radius: 6px; margin-right: 8px;
}
.practice .board-canvas { cursor: pointer; }
.practice-status { min-height: 26px; margin-top: 8px; }
.practice-status .pass { color: var(--accent); font-weight: 700; font-size: 17px; }
.practice-ctrl {
  display: flex; align-items: center; gap: 16px; margin-top: 10px;
  font-size: 14px; color: #555;
}
.practice-ctrl .turn { font-weight: 600; }
.practice-ctrl button { margin-left: auto; }

.nav-row { display: flex; justify-content: space-between; margin-top: 34px; }

@media (max-width: 760px) {
  .topbar { padding: 10px 12px; }
  .topbar .brand { font-size: 15px; }
  .topbar .account { gap: 6px; }
  .topbar .account button { padding: 7px 10px; }
  #user-label { display: none; }
  .layout { flex-direction: column; }
  .sidebar { width: 100%; position: static; }
  .content { padding: 18px; }
}