:root {
  --sidebar-w: 248px;
  --bg: #f7f8fa;
  --panel: #ffffff;
  --text: #1f2933;
  --muted: #6b7785;
  --line: #e3e7ec;
  --accent: #2563eb;
  --accent-soft: #e8efff;
  --side-bg: #111827;
  --side-text: #d1d5db;
  --side-muted: #8b95a5;
  --side-hover: #1f2937;
}

* { box-sizing: border-box; }

html, body { margin: 0; }

body {
  font-family: "Noto Sans TC", "Microsoft JhengHei", "PingFang TC", system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
}

/* ---------- 左側功能表 ---------- */
.sidebar {
  position: fixed;
  inset: 0 auto 0 0;
  width: var(--sidebar-w);
  background: var(--side-bg);
  color: var(--side-text);
  overflow-y: auto;
  padding: 20px 12px 40px;
  z-index: 20;
  transition: transform 0.2s ease;
}

.brand {
  display: block;
  color: #fff;
  font-size: 1.25rem;
  font-weight: 700;
  text-decoration: none;
  padding: 4px 12px 18px;
  border-bottom: 1px solid #263041;
  margin-bottom: 12px;
}

.menu, .sub { list-style: none; margin: 0; padding: 0; }

.cat-btn {
  width: 100%;
  display: flex;
  align-items: baseline;
  gap: 8px;
  background: none;
  border: 0;
  color: #fff;
  font: inherit;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-align: left;
  padding: 10px 12px;
  border-radius: 6px;
  cursor: pointer;
}
.cat-btn:hover { background: var(--side-hover); }
.cat-btn::before {
  content: "";
  width: 4px; height: 16px;
  border-radius: 2px;
  background: var(--c, var(--accent));
  align-self: center;
  flex: none;
}
a.cat-btn { text-decoration: none; }
a.cat-btn.active { background: var(--c, var(--accent)); }
a.cat-btn.active::before { background: #fff; }
a.cat-btn.active small { color: #dbe6ff; }
.cat-btn small { color: var(--side-muted); font-weight: 400; font-size: 0.8rem; letter-spacing: 0; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; min-width: 0; }
.arrow {
  margin-left: auto;
  width: 7px; height: 7px;
  border-right: 2px solid var(--side-muted);
  border-bottom: 2px solid var(--side-muted);
  transform: rotate(-45deg);
  transition: transform 0.15s;
  align-self: center;
}
.cat.open .arrow { transform: rotate(45deg); }

.sub { display: none; padding: 2px 0 8px; }
.cat.open .sub { display: block; }

.sub a {
  display: block;
  color: var(--side-text);
  text-decoration: none;
  padding: 6px 12px 6px 28px;
  border-radius: 6px;
  font-size: 0.95rem;
}
.sub a:hover { background: var(--side-hover); color: #fff; }
.sub a.active { background: var(--c, var(--accent)); color: #fff; }

/* ---------- 主內容 ---------- */
.content {
  margin-left: var(--sidebar-w);
  padding: 48px 56px 80px;
  max-width: calc(var(--sidebar-w) + 960px);
}

.breadcrumb { color: var(--muted); font-size: 0.9rem; margin-bottom: 6px; }
.breadcrumb a { color: var(--muted); }

h1 { font-size: 2rem; margin: 0 0 8px; line-height: 1.3; }
h2 { font-size: 1.35rem; margin: 32px 0 8px; }
.lead { color: var(--muted); margin: 0 0 28px; }

.placeholder {
  background: var(--panel);
  border: 1px dashed #c5cdd8;
  border-radius: 10px;
  padding: 24px 28px;
  color: var(--muted);
}
.placeholder ul { margin: 8px 0 0; padding-left: 1.2em; }

.card-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
}
.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-top: 5px solid var(--c, var(--accent));
  border-radius: 10px;
  padding: 18px 20px;
}
.card h2 { margin: 0; font-size: 1.2rem; color: var(--c, var(--text)); }
.card p { margin: 2px 0 12px; color: var(--muted); font-size: 0.9rem; }
.levels { display: flex; gap: 8px; flex-wrap: wrap; }
.levels a {
  background: color-mix(in srgb, var(--c, var(--accent)) 12%, #fff);
  color: var(--c, var(--accent));
  text-decoration: none;
  padding: 3px 12px;
  border-radius: 999px;
  font-size: 0.9rem;
}
.levels a:hover { background: var(--c, var(--accent)); color: #fff; }

/* ---------- 手機版 ---------- */
.menu-toggle, .backdrop { display: none; }

@media (max-width: 980px) {
  .card-grid { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 820px) {
  .sidebar { transform: translateX(-100%); }
  .nav-open .sidebar { transform: none; }
  .brand { padding-left: 52px; }
  .content { margin-left: 0; padding: 72px 16px 60px; }
  .card-grid { grid-template-columns: 1fr; }
  .menu-toggle {
    display: flex; flex-direction: column; justify-content: center; gap: 4px;
    position: fixed; top: 14px; left: 14px; z-index: 30;
    width: 40px; height: 40px; padding: 0 10px;
    border: 1px solid var(--line); border-radius: 8px; background: var(--panel);
    cursor: pointer;
  }
  .menu-toggle span { display: block; height: 2px; background: var(--text); border-radius: 2px; }
  .nav-open .backdrop { display: block; position: fixed; inset: 0; background: rgba(0,0,0,0.35); z-index: 10; }
}

/* ---------- 課程清單 ---------- */
.lesson-list { list-style: none; margin: 0; padding: 0; display: grid; gap: 12px; }
.lesson-list a {
  display: flex; gap: 14px; align-items: baseline;
  background: var(--panel);
  border: 1px solid var(--line);
  border-left: 4px solid var(--c, var(--accent));
  border-radius: 10px;
  padding: 14px 18px;
  color: var(--text);
  text-decoration: none;
}
.lesson-list a:hover { border-color: var(--c, var(--accent)); }
.lesson-code { font-family: ui-monospace, Consolas, monospace; font-size: 0.85rem; color: var(--c, var(--accent)); white-space: nowrap; }
.lesson-title { font-weight: 600; }