/* ============================================================
   ONZUME NAV — vertical left rail, collapsible, multi-page.
   Loaded AFTER the page's :root tokens. Requires the page to
   define: --paper, --ink, --red, --muted. And a JetBrains
   Mono family for the monospace nav text.

   Markup contract:
     <a href="#main" class="sr-only">SKIP TO CONTENT</a>
     <nav class="navbar" id="navbar" data-current-page="file.html">
       <div class="nav-head">...</div>
       <div class="nav-group"> [PAGES] <ul data-list="pages">...</ul> </div>
       <div class="nav-group"> [SECTIONS] <ul data-list="sections">...</ul> </div>
       <div class="nav-foot">...</div>
     </nav>
     <button class="nav-toggle-edge" id="nav-toggle" ...></button>
     <div class="nav-mobile-backdrop" id="nav-backdrop"></div>
     <div class="layout"> [page content] </div>
   ============================================================ */

.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}
.sr-only:focus {
  position: fixed;
  top: 8px; left: 8px;
  width: auto; height: auto;
  padding: 8px 12px;
  clip: auto;
  background: var(--ink);
  color: var(--paper);
  z-index: 9999;
  font: 11px/1 'JetBrains Mono', ui-monospace, monospace;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  text-decoration: none;
}

.layout {
  margin-left: 240px;
  transition: margin-left 0ms;
}
body.nav-collapsed .layout { margin-left: 48px; }

.navbar {
  position: fixed;
  left: 0;
  top: 36px;
  bottom: 0;
  width: 240px;
  background: var(--paper);
  border-right: 2px solid var(--ink);
  z-index: 90;
  display: flex;
  flex-direction: column;
  font-family: 'JetBrains Mono', ui-monospace, Menlo, monospace;
  overflow: hidden;
  will-change: transform;
}
.navbar.collapsed { width: 48px; }

.nav-toggle-edge {
  position: fixed;
  top: 50%;
  left: 222px;
  transform: translateY(-50%);
  width: 36px;
  height: 36px;
  background: var(--ink);
  color: var(--paper);
  border: 1px solid var(--ink);
  font-family: 'JetBrains Mono', monospace;
  font-size: 14px;
  font-weight: 700;
  cursor: pointer;
  z-index: 250;
  padding: 0;
  display: grid;
  place-items: center;
  line-height: 1;
  text-transform: uppercase;
}
.nav-toggle-edge::before { content: '◀'; }
body.nav-collapsed .nav-toggle-edge { left: 30px; }
body.nav-collapsed .nav-toggle-edge::before { content: '▶'; }
.nav-toggle-edge:hover { background: var(--red); border-color: var(--red); }
.nav-toggle-edge:focus-visible {
  outline: 2px solid var(--red);
  outline-offset: 2px;
}

.nav-group {
  display: flex;
  flex-direction: column;
  border-bottom: 1px solid var(--ink);
  flex: 0 0 auto;
  min-height: 0;
}
.nav-group.nav-group-sections {
  flex: 1 1 auto;
}
.navbar.collapsed .nav-group { border-bottom-color: transparent; }
.nav-group:empty { display: none; }

.nav-group-label {
  padding: 10px 14px 6px;
  font-size: 9px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--red);
  font-weight: 700;
  background: var(--paper);
  border-bottom: 1px solid var(--ink);
}
.navbar.collapsed .nav-group-label { display: none; }

.nav-list {
  flex: 0 1 auto;
  overflow-y: auto;
  padding: 0;
  margin: 0;
  list-style: none;
  display: flex;
  flex-direction: column;
  scrollbar-width: thin;
  scrollbar-color: var(--ink) var(--paper);
}
.nav-group-sections .nav-list { flex: 1 1 auto; min-height: 0; }
.nav-list::-webkit-scrollbar { width: 6px; }
.nav-list::-webkit-scrollbar-track { background: var(--paper); }
.nav-list::-webkit-scrollbar-thumb { background: var(--ink); }

.nav-section, .nav-page {
  display: flex;
  align-items: stretch;
  border-bottom: 1px solid var(--ink);
  background: var(--paper);
  color: var(--ink);
  cursor: pointer;
  text-decoration: none;
  border-left: 0 solid var(--red);
  position: relative;
  font-family: inherit;
  font-size: inherit;
  line-height: 1;
}
.nav-section:last-child, .nav-page:last-child { border-bottom: 0; }
.nav-section:hover, .nav-page:hover { background: var(--ink); color: var(--paper); }
.nav-section:focus-visible, .nav-page:focus-visible {
  outline: 2px solid var(--red);
  outline-offset: -2px;
  z-index: 1;
}
.nav-section.active, .nav-page.active {
  background: var(--ink);
  color: var(--paper);
  border-left: 4px solid var(--red);
}
.nav-section.active::after, .nav-page.active::after {
  content: '●';
  position: absolute;
  right: 10px;
  top: 50%;
  transform: translateY(-50%);
  color: var(--red);
  font-size: 8px;
  line-height: 1;
}
.nav-section.active .nav-num, .nav-page.active .nav-num {
  color: var(--red);
}

.nav-num {
  width: 36px;
  flex: 0 0 36px;
  display: grid;
  place-items: center;
  border-right: 1px solid var(--ink);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.04em;
  padding: 12px 0;
  background: var(--paper);
  color: var(--ink);
  font-variant-numeric: tabular-nums;
}
.nav-section:hover .nav-num, .nav-section.active .nav-num,
.nav-page:hover .nav-num, .nav-page.active .nav-num {
  background: var(--ink);
  color: var(--paper);
  border-right-color: var(--paper);
}
.navbar.collapsed .nav-num { width: 100%; flex: 1; font-size: 12px; }

.nav-label {
  flex: 1;
  padding: 12px 12px;
  font-size: 10px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  font-weight: 700;
  display: flex;
  align-items: center;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  min-width: 0;
}
.navbar.collapsed .nav-label { display: none; }

.nav-foot {
  padding: 12px 14px;
  border-top: 1px solid var(--ink);
  font-size: 9px;
  letter-spacing: 0.1em;
  line-height: 1.7;
  text-transform: uppercase;
  color: var(--muted);
  flex: 0 0 auto;
}
.nav-foot .red { color: var(--red); font-weight: 700; }
.navbar.collapsed .nav-foot { display: none; }

.nav-mobile-backdrop {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(5, 5, 5, 0.55);
  z-index: 89;
  cursor: pointer;
}
body.nav-open .nav-mobile-backdrop { display: block; }

@media (max-width: 900px) {
  .layout, body.nav-collapsed .layout { margin-left: 0; }
  .navbar {
    top: 0;
    z-index: 200;
    transform: translateX(-100%);
    width: 240px;
    border-right: 2px solid var(--ink);
    box-shadow: 0 0 0 1px var(--ink);
  }
  .navbar.collapsed { transform: translateX(-100%); width: 240px; }
  body.nav-open .navbar { transform: translateX(0); }
  body.nav-open { overflow: hidden; }
  .nav-toggle-edge {
    top: 4px;
    left: 4px;
    transform: none;
    width: 32px;
    height: 32px;
    font-size: 13px;
    z-index: 260;
  }
  body.nav-open .nav-toggle-edge {
    top: 4px;
    right: 4px;
    left: auto;
    transform: none;
  }
  body.nav-open .nav-toggle-edge::before { content: '✕'; }
}