/* 应用外壳:顶栏 + 侧栏 + 正文 */
.topbar {
  position: sticky; top: 0; z-index: 30;
  display: flex; align-items: center; gap: 12px;
  height: 52px; padding: 0 16px;
  padding-left: calc(16px + env(safe-area-inset-left));
  padding-right: calc(16px + env(safe-area-inset-right));
  background: var(--paper);
  border-bottom: 1px solid var(--line);
}
.topbar .brand {
  font-weight: 600; font-size: 15px; text-decoration: none; color: var(--ink);
  white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
}
.topbar .spacer { flex: 1; }

.icon-btn {
  display: inline-flex; align-items: center; justify-content: center;
  min-width: 44px; min-height: 44px;
  border-radius: var(--radius-ctl);
  color: var(--ink-2);
  -webkit-tap-highlight-color: transparent;
}
.icon-btn:active { color: var(--ink); background: var(--accent-soft); }
@media (hover: hover) and (pointer: fine) {
  .icon-btn:hover { color: var(--ink); background: var(--accent-soft); }
}
.icon-btn svg { width: 22px; height: 22px; }
.icon-btn .theme-ico { display: inline-flex; }

.shell { display: flex; min-height: calc(100vh - 52px); }

/* 侧栏(桌面常驻,移动为抽屉) */
.sidenav {
  width: var(--sidebar-w); flex-shrink: 0;
  border-right: 1px solid var(--line);
  padding: 16px 0 48px;
  position: sticky; top: 52px;
  height: calc(100vh - 52px);
  overflow-y: auto;
  background: var(--paper);
}
.sidenav .nav-group { margin-bottom: 4px; }
.sidenav .nav-ch {
  display: flex; align-items: baseline; gap: 8px; width: 100%;
  padding: 8px 16px; font-size: 14px; text-align: left;
  color: var(--ink); border-radius: 0;
}
.sidenav .nav-ch:hover { background: var(--accent-soft); }
.sidenav .nav-ch .ch-num { color: var(--ink-2); font-variant-numeric: tabular-nums; flex-shrink: 0; width: 1.6em; }
.sidenav .nav-ch .done-mark { margin-left: auto; color: var(--ok); flex-shrink: 0; }
.sidenav .nav-secs { margin: 0; padding: 0 0 8px; list-style: none; }
.sidenav .nav-secs a {
  display: block; padding: 6px 16px 6px 46px;
  font-size: 13.5px; color: var(--ink-2); text-decoration: none;
  border-left: 2px solid transparent;
}
.sidenav .nav-secs a:hover { color: var(--ink); }
.sidenav .nav-secs a[aria-current="page"] {
  color: var(--accent); border-left-color: var(--accent);
  background: var(--accent-soft); font-weight: 600;
}
.sidenav .nav-util { border-top: 1px solid var(--line); margin-top: 16px; padding-top: 8px; }
.sidenav .nav-util a {
  display: block; padding: 8px 16px; font-size: 14px;
  color: var(--ink-2); text-decoration: none;
}
.sidenav .nav-util a:hover { color: var(--ink); background: var(--accent-soft); }
.sidenav .nav-util a[aria-current="page"] { color: var(--accent); font-weight: 600; }

/* 正文 */
/* 正文列:纵向 flex,让 footer 只落在正文下方而非横跨 sidenav */
.main-col {
  flex: 1; min-width: 0;
  display: flex; flex-direction: column;
}
.main {
  flex: 1 0 auto;
  padding: 32px 24px 64px;
}
.content { max-width: var(--measure); margin: 0 auto; }

/* 抽屉遮罩 */
.scrim {
  position: fixed; inset: 0; z-index: 40;
  background: rgba(0, 0, 0, 0.4);
  opacity: 0; pointer-events: none;
  transition: opacity var(--speed) ease;
}
.scrim.open { opacity: 1; pointer-events: auto; }

/* 移动抽屉形态在 responsive.css 中定义 */

/* 上一节/下一节 */
.pager {
  display: flex; gap: 12px; justify-content: space-between;
  margin-top: 48px; padding-top: 24px; border-top: 1px solid var(--line);
}
.pager a {
  flex: 1; max-width: 48%;
  text-decoration: none; padding: 12px 16px;
  border: 1px solid var(--line); border-radius: var(--radius-panel);
  color: var(--ink);
}
.pager a:hover { border-color: var(--accent); }
.pager .dir { display: block; font-size: 13px; color: var(--ink-2); }
.pager .next { text-align: right; margin-left: auto; }

/* 章节页头 */
.lesson-head { margin-bottom: 32px; }
.lesson-head .crumb { font-size: 14px; color: var(--ink-2); margin-bottom: 4px; }
.lesson-head .verify-date {
  display: flex; align-items: center; flex-wrap: wrap; gap: 8px;
  font-size: 13px; color: var(--ink-2); margin-top: 8px;
}

/* 页脚:位于正文列(.main-col)底部,不横跨侧栏 */
.site-foot {
  flex-shrink: 0;
  border-top: 1px solid var(--line);
  padding: 24px;
  padding-bottom: calc(24px + env(safe-area-inset-bottom));
  font-size: 13px; color: var(--ink-2);
  text-align: center;
}