.sidebar { position: sticky; top: 0; display: flex; height: 100dvh; min-height: 0; flex-direction: column; gap: 26px; align-self: start; overflow-y: auto; background: var(--color-surface-muted); padding: 24px 14px; scrollbar-width: thin; scrollbar-color: #c5c9cf transparent; }
.sidebar__brand { display: flex; align-items: center; justify-content: space-between; }
.sidebar__footer { margin-top: auto; padding: 20px 10px 0; }
.sidebar__footer > p { margin-top: 12px; color: var(--color-text-muted); font-size: 0.75rem; }
.sidebar-drawer > summary { display: none; }
.sidebar__intro h2 { padding: 0 10px; color: var(--color-text-muted); font-size: 0.6875rem; font-weight: 500; }
.lesson-nav { display: grid; gap: 20px; margin-top: 12px; }
.lesson-nav__group h3 { margin-bottom: 4px; padding: 0 10px; font-size: 0.875rem; font-weight: 500; }
.lesson-nav__stage > summary { display: flex; min-height: 44px; align-items: center; justify-content: space-between; gap: 6px; padding: 8px 10px; cursor: pointer; color: var(--color-text-muted); font-size: 0.6875rem; list-style: none; }
.lesson-nav__stage > summary > span { min-width: 0; }
.lesson-nav__stage > summary::-webkit-details-marker { display: none; }
.lesson-nav__stage > summary::after { content: "+"; }
.lesson-nav__stage[open] > summary::after { content: "−"; }
.lesson-nav__stage > summary small { margin-left: auto; font-size: 0.6875rem; font-variant-numeric: tabular-nums; white-space: nowrap; }
.lesson-nav__stage-body { display: grid; gap: 2px; }
.lesson-nav__link { display: flex; min-height: 44px; align-items: center; justify-content: space-between; gap: 8px; padding: 8px 10px; color: var(--color-text-muted); font-size: 0.75rem; text-decoration: none; overflow-wrap: anywhere; }
.lesson-nav__link--active { background: var(--color-accent-soft); color: var(--color-text); }
.lesson-nav__status { color: var(--color-success); font-size: 0.6875rem; white-space: nowrap; }
@media (max-width: 820px) {
  .sidebar { position: static; display: grid; grid-template-columns: minmax(0, 1fr) auto; height: auto; gap: 0 8px; overflow: visible; padding: 8px var(--shell-padding); }
  .sidebar__brand { grid-column: 1; grid-row: 1; }
  .site-navigation { display: contents; }
  .site-navigation > summary { grid-column: 2; grid-row: 1; }
  .site-nav, #lesson-nav { grid-column: 1 / -1; }
  .site-navigation:not([open]) > .site-nav { display: none; }
  .sidebar__footer { display: block; grid-column: 1 / -1; margin-top: 0; padding: 0 0 4px; }
  .sidebar__footer > p { display: none; }
  .sidebar-drawer > summary { display: flex; min-height: 44px; align-items: center; justify-content: space-between; gap: 8px; cursor: pointer; color: var(--color-text); font-size: 0.75rem; list-style: none; }
  .sidebar-drawer > summary::-webkit-details-marker { display: none; }
  .sidebar-drawer > summary::after { content: "+"; }
  .sidebar-drawer[open] > summary::after { content: "−"; }
  .sidebar-drawer__content { padding: 12px 0; }
  .lesson-nav { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (min-width: 1200px) { .sidebar { padding-inline: 18px; } .lesson-nav__link { font-size: 0.8125rem; } }
@media (max-width: 560px) { .lesson-nav { grid-template-columns: minmax(0, 1fr); } }