:root { --nav-w: 340px; --nav-rail-w: 72px; }

body { padding-left: var(--nav-w); transition: padding-left .2s ease; }

.course-nav {
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  width: var(--nav-w);
  background: #fff;
  border-right: 1.5px solid var(--line);
  overflow-x: hidden;
  overflow-y: auto;
  z-index: 40;
  transition: width .2s ease, transform .2s ease;
}

.nav-collapse {
  position: fixed;
  z-index: 41;
  left: calc(var(--nav-w) - 16px);
  bottom: 28px;
  width: 32px;
  height: 32px;
  padding: 0;
  border-radius: 50%;
  border: 1.5px solid var(--line);
  background: #fff;
  color: var(--navy);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  box-shadow: 0 1px 2px rgba(27, 58, 91, .06), 0 4px 12px rgba(27, 58, 91, .1);
  transition: left .2s ease, width .2s ease, height .2s ease;
}
.nav-collapse svg { display: block; transition: transform .2s ease; }
.nav-collapse:hover { border-color: var(--teal); color: var(--teal); }
.nav-collapse:focus-visible { outline: 3px solid var(--bright); outline-offset: 2px; }
body.nav-collapsed .nav-collapse { left: calc(var(--nav-rail-w) - 16px); }
body.nav-collapsed .nav-collapse svg { transform: rotate(180deg); }

.nav-head {
  position: sticky;
  top: 0;
  z-index: 1;
  background: #fff;
  border-bottom: 1.5px solid var(--line);
}
.nav-brand {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 6px;
  padding: 18px 16px 8px;
  text-decoration: none;
}
.nav-brand img { height: 44px; width: auto; max-width: 100%; display: block; }
.nav-brand .nav-brand-mark { display: none; }
.nav-brand .from {
  font-size: 9.5px;
  letter-spacing: .13em;
  text-transform: uppercase;
  font-weight: 600;
  color: var(--teal);
}

.nav-close {
  display: none;
  position: absolute;
  top: 12px;
  right: 12px;
  width: 32px;
  height: 32px;
  border-radius: 8px;
  border: 1.5px solid var(--line);
  background: #fff;
  color: var(--navy);
  align-items: center;
  justify-content: center;
  cursor: pointer;
}
.nav-close:focus-visible { outline: 3px solid var(--bright); outline-offset: 2px; }

.nav-icons {
  display: flex;
  flex-direction: column;
  gap: 2px;
  margin: 2px 10px 12px;
}
.nav-icon {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 10px;
  border-radius: 10px;
  text-decoration: none;
  font-size: 13px;
  font-weight: 600;
  line-height: 1.3;
  color: var(--navy);
}
.nav-icon svg { display: block; flex: none; color: var(--teal); }
.nav-icon:hover { background: var(--cream); }
.nav-icon:focus-visible { outline: 3px solid var(--bright); outline-offset: 2px; }
.nav-icon.on {
  background: #e8f1ef;
  box-shadow: inset 3px 0 0 var(--teal);
}

.nav-mods { display: flex; flex-direction: column; gap: 2px; padding: 10px 10px 28px; }
.nav-categories-toggle, .nav-categories-heading { display: none; }

.nav-mod summary {
  list-style: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 10px;
  border-radius: 10px;
  font-size: 13px;
  font-weight: 600;
  line-height: 1.3;
  color: var(--navy);
}
.nav-mod summary::-webkit-details-marker { display: none; }
.nav-mod summary:hover { background: var(--cream); }
.nav-mod summary:focus-visible { outline: 3px solid var(--bright); outline-offset: 2px; }
.nav-mod[open] > summary { background: #f4f8f7; }
.nav-num {
  flex: none;
  width: 22px;
  font-size: 11px;
  font-weight: 700;
  color: var(--teal);
  font-variant-numeric: tabular-nums;
}
.nav-name { flex: 1; min-width: 0; }
.nav-chev { flex: none; color: var(--ink-soft); transition: transform .18s; }
.nav-mod[open] .nav-chev { transform: rotate(180deg); }

.nav-lessons { display: flex; flex-direction: column; padding: 2px 0 8px 28px; }
.nav-lesson {
  display: flex;
  gap: 8px;
  align-items: flex-start;
  padding: 7px 10px;
  border-radius: 8px;
  text-decoration: none;
  color: var(--slate);
  font-size: 12.5px;
  line-height: 1.4;
  font-weight: 500;
}
.nav-lesson:hover { background: var(--cream); color: var(--navy); }
.nav-lesson:focus-visible { outline: 3px solid var(--bright); outline-offset: -3px; }
.nav-lesson.on {
  background: #e8f1ef;
  color: var(--navy);
  font-weight: 600;
  box-shadow: inset 3px 0 0 var(--teal);
}
.nav-ln {
  flex: none;
  width: 40px;
  font-size: 10.5px;
  font-weight: 700;
  color: var(--ink-soft);
  font-variant-numeric: tabular-nums;
  padding-top: 1px;
}
.nav-lesson.on .nav-ln { color: var(--teal); }

.nav-bar { display: none; }
.nav-backdrop { display: none; }

@media (min-width: 961px) {
  body.nav-collapsed { padding-left: var(--nav-rail-w); }
  body.nav-collapsed .course-nav { width: var(--nav-rail-w); overflow: visible; }
  body.nav-collapsed .nav-brand { align-items: center; padding: 18px 12px 12px; }
  body.nav-collapsed .nav-brand > img:not(.nav-brand-mark),
  body.nav-collapsed .nav-brand .from { display: none; }
  body.nav-collapsed .nav-brand .nav-brand-mark { display: block; width: 36px; height: 36px; object-fit: contain; }
  body.nav-collapsed .nav-icons { margin: 2px 12px 14px; gap: 6px; }
  body.nav-collapsed .nav-icon { justify-content: center; min-height: 44px; padding: 10px 0; gap: 0; }
  body.nav-collapsed .nav-icon svg { width: 20px; height: 20px; }
  body.nav-collapsed .nav-label {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip-path: inset(50%);
    white-space: nowrap;
  }
  body.nav-collapsed .nav-categories { padding: 12px; }
  body.nav-collapsed .nav-categories-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 100%;
    height: 44px;
    border: 0;
    border-radius: 10px;
    background: transparent;
    color: var(--teal);
    cursor: pointer;
  }
  body.nav-collapsed .nav-categories-toggle:hover,
  body.nav-collapsed .nav-categories.is-open .nav-categories-toggle { background: #e8f1ef; }
  .nav-categories-toggle:focus-visible { outline: 3px solid var(--bright); outline-offset: 2px; }
  body.nav-collapsed .nav-mods {
    display: none;
    position: fixed;
    top: var(--categories-top, 228px);
    left: var(--nav-rail-w);
    width: 320px;
    max-height: calc(100dvh - var(--categories-top, 228px) - 16px);
    overflow-y: auto;
    overscroll-behavior: contain;
    padding: 12px;
    background: #fff;
    border: 1.5px solid var(--line);
    border-radius: 14px;
    box-shadow: 0 8px 32px rgba(27, 58, 91, .14);
  }
  body.nav-collapsed .nav-categories.is-open .nav-mods { display: flex; }
  body.nav-collapsed .nav-categories-heading {
    display: block;
    padding: 6px 10px 12px;
    font-size: 10px;
    font-weight: 600;
    letter-spacing: .12em;
    text-transform: uppercase;
    color: var(--ink-soft);
  }
  body.nav-collapsed .nav-mod.is-active > summary { background: #e8f1ef; box-shadow: inset 3px 0 0 var(--teal); }
}

@media (max-width: 960px) {
  body { padding-left: 0; }
  .nav-collapse { display: none; }
  .nav-bar {
    display: flex;
    position: sticky;
    top: 0;
    z-index: 20;
    background: var(--cream);
    padding: 10px 16px;
    border-bottom: 1.5px solid var(--line);
  }
  .nav-toggle {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    font-family: inherit;
    font-size: 13px;
    font-weight: 600;
    color: var(--navy);
    background: #fff;
    border: 1.5px solid var(--line);
    border-radius: 999px;
    padding: 8px 14px;
    cursor: pointer;
  }
  .nav-toggle:focus-visible { outline: 3px solid var(--bright); outline-offset: 2px; }
  .course-nav {
    width: min(var(--nav-w), 88vw);
    transform: translateX(-105%);
    transition: transform .2s ease;
  }
  .course-nav.is-open { transform: none; box-shadow: 8px 0 28px rgba(27, 58, 91, .16); }
  .nav-close { display: flex; }
  .nav-brand { padding-right: 52px; }
  .nav-backdrop {
    position: fixed;
    inset: 0;
    background: rgba(27, 58, 91, .35);
    z-index: 30;
  }
  .nav-backdrop:not([hidden]) { display: block; }
}

@media (prefers-reduced-motion: reduce) {
  .nav-chev, .course-nav, .nav-collapse, .nav-collapse svg, body { transition: none !important; }
}