/* Tree-nav sidebar navigation styles (shared across chapters). */
.tree-nav {
    position: relative;
}

.tree-nav svg.tree-lines {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 0;
    overflow: visible;
}

.tree-nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
    position: relative;
    z-index: 1;
}

.tree-nav li {
    margin-bottom: 0;
    position: relative;
}

.tree-nav a[data-level] {
    display: block;
    text-decoration: none;
    border-radius: 4px;
    transition: color 0.2s, background-color 0.2s;
    line-height: 1.5;
    position: relative;
    z-index: 1;
}

.tree-nav a[data-level="h3"] {
    font-size: 13px;
    font-weight: 500;
    color: var(--vp-c-text-1);
    padding: 5px 8px 5px 28px;
}

.tree-nav a[data-level="h4"] {
    font-size: 12.5px;
    font-weight: 400;
    color: var(--vp-c-text-2);
    padding: 4px 8px 4px 44px;
}

.tree-nav a[data-level]:hover {
    color: var(--tn-accent);
    background: var(--tn-accent-soft);
}

.tree-nav a[data-level].active {
    color: var(--tn-accent);
    font-weight: 600;
}

/* SVG elements */
.tree-dot {
    fill: var(--tn-dot-fill);
    stroke: var(--tn-line);
    stroke-width: 1.5;
    transition: fill 0.2s, stroke 0.2s;
}
.tree-dot.active {
    fill: var(--tn-accent);
    stroke: var(--tn-accent);
}
.tree-trunk {
    fill: none;
    stroke: var(--tn-line);
    stroke-width: 1.5;
    stroke-linecap: round;
    transition: stroke 0.2s;
}
.tree-trunk.active {
    stroke: var(--tn-accent);
}
.tree-branch.active {
    stroke: var(--tn-accent);
    stroke-linecap: round;
}
.tree-branch {
    fill: none;
    stroke: var(--tn-line-child);
    stroke-width: 1;
    stroke-dasharray: 3 2;
    stroke-linecap: round;
    transition: stroke 0.2s;
}

/* Prev/Next chapter navigation (above TOC) */
.chapter-nav {
    display: flex;
    gap: 8px;
    margin-bottom: 16px;
}
.chapter-nav-btn {
    flex: 1;
    text-align: center;
    font-size: 13px;
    line-height: 1.4;
    padding: 6px 8px;
    border: 1px solid var(--vp-c-brand-1, #d95c41);
    border-radius: 6px;
    color: var(--vp-c-brand-1, #d95c41);
    text-decoration: none;
    white-space: nowrap;
    transition: background 0.15s, color 0.15s;
}
.chapter-nav-btn:hover {
    background: var(--vp-c-brand-1, #d95c41);
    color: #fff;
}
.chapter-nav-btn.disabled {
    opacity: 0.35;
    pointer-events: none;
    border-color: var(--vp-c-divider, #e2e2e3);
    color: var(--vp-c-text-3, #999);
}