/* Navigation tree: every destination uses the same component structure. */
  .tabs {
    --nav-axis: 13px;
    --nav-marker-size: calc(var(--nav-axis) * 2);
    --nav-line: 1px;
    --nav-active-line: 2px;
    position: sticky;
    top: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 0;
    max-height: calc(100vh - 3rem);
    padding: 0;
    border: 0;
    overflow-y: auto;
    scrollbar-width: thin;
    scrollbar-color: var(--color-scrollbar) transparent;
  }
  .nav-track {
    position: absolute;
    z-index: 2;
    top: 0;
    left: 0;
    display: block;
    overflow: visible;
    pointer-events: none;
  }
  .nav-track path {
    fill: none;
    vector-effect: non-scaling-stroke;
  }
  .nav-track-base {
    stroke: #8fcac7;
    stroke-width: var(--nav-line);
  }
  .nav-track-active {
    stroke: #d45e6a;
    stroke-width: var(--nav-active-line);
  }
  .nav-group { display: grid; gap: 0; min-width: 0; }
  .nav-group + .nav-group { margin-top: 0.55rem; }
  .nav-group-label,
  .nav-item-root {
    display: grid;
    grid-template-columns: var(--nav-marker-size) minmax(0, 1fr);
    gap: 0.5rem;
    align-items: center;
  }
  .nav-group-label {
    position: relative;
    min-height: 18px;
    margin: 0.55rem 0 0.1rem;
    color: #879293;
    font: 600 0.58rem/1 var(--font-mono);
    letter-spacing: 0.08em;
    text-transform: uppercase;
  }
  .nav-group:first-child .nav-group-label { margin-top: 0; }
  .nav-group-label > span {
    position: relative;
    z-index: 3;
    justify-self: center;
    width: 8px;
    height: 8px;
    border: 1px solid #9ececc;
    border-radius: 2px;
    background: var(--color-bg);
  }
  .nav-item {
    position: relative;
    min-width: 0;
    border-radius: 6px;
    color: var(--color-text);
    text-align: left;
    transition: background-color 140ms ease, box-shadow 160ms ease, color 140ms ease, opacity 140ms ease;
  }
  .tabs a:hover { opacity: 1; }
  .nav-item:hover { background: #edf6f5; }
  .nav-item[aria-current="location"] { background: transparent; }
  .nav-item:not([aria-current="location"]) .nav-copy { opacity: 0.68; }
  .nav-branch:has(.nav-item-child[aria-current="location"]) > .nav-item-root .nav-copy { opacity: 1; }
  .nav-item-root { min-height: 40px; padding: 0.25rem 0.45rem 0.25rem 0; }
  .nav-marker {
    position: relative;
    z-index: 3;
    display: grid;
    width: var(--nav-marker-size);
    height: var(--nav-marker-size);
    place-items: center;
    border: 1px solid #9ececc;
    border-radius: 50%;
    background: var(--color-bg);
    color: #5c8987;
    font: 0.58rem/1 var(--font-mono);
  }
  .nav-item[aria-current="location"] .nav-marker {
    border-color: #e27680;
    color: #d90000;
  }
  .nav-branch:has(.nav-item-child[aria-current="location"]) > .nav-item-root .nav-marker {
    border-color: #e27680;
    color: #b44a55;
  }
  .nav-copy { display: grid; gap: 0.05rem; min-width: 0; }
  .nav-copy strong { overflow: hidden; font-size: 0.75rem; font-weight: 650; line-height: 1.2; text-overflow: ellipsis; }
  .nav-copy small { overflow: hidden; color: var(--color-text-secondary); font: 0.57rem/1.3 var(--font-mono); text-overflow: ellipsis; }
  .nav-branch { min-width: 0; }
  .nav-children {
    display: grid;
    margin-left: var(--nav-axis);
  }
  .nav-item-child {
    display: block;
    min-height: 30px;
    padding: 0.2rem 0.4rem 0.2rem calc(var(--nav-axis) + 8px);
  }
  .nav-item-child .nav-copy strong { font-size: 0.68rem; font-weight: 600; }
  .nav-item-child .nav-copy small { font-size: 0.52rem; }

  @media (max-width: 980px) {
    .tabs {
      position: static;
      display: grid;
      grid-template-columns: repeat(2, minmax(0, 1fr));
      gap: 1rem;
      max-height: none;
      overflow: visible;
    }
    .nav-track { display: none; }
  }

  @media (max-width: 640px) {
    .tabs { grid-template-columns: 1fr; }
  }