/* ════════════════════════════════════════
   側欄
   ════════════════════════════════════════ */
#sidebar {
    position: fixed;
    left: 0;
    top: 0;
    width: 60px;
    height: 100vh;
    background: var(--surface);
    border-right: 1px solid var(--accent-bg);
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 10px 8px;
    gap: 4px;
    z-index: 1000;
    overflow: hidden;
    transition: width 0.25s cubic-bezier(0.4, 0, 0.2, 1),
                background-color 0.25s ease;
}
#sidebar.expanded {
    width: 220px;
}

/* ── 側欄頂部：標題 + toggle 按鈕 ── */
#sidebar-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    overflow: hidden;
    flex-shrink: 0;
}

#sidebar-title {
    font-family: "Noto Serif TC", serif;
    font-size: 0.72rem;
    font-weight: 500;
    color: var(--ink);
    letter-spacing: 0.02em;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    flex: 1;
    min-width: 0;
    padding-left: 4px;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.2s 0.1s;
}
#sidebar.expanded #sidebar-title {
    opacity: 1;
}

/* ── 分隔線 ── */
.nav-divider {
    width: 100%;
    height: 1px;
    background: var(--accent-bg);
    margin: 4px 0;
    flex-shrink: 0;
}

/* ── 推到底部的彈性空白 ── */
.nav-spacer {
    flex: 1;
}

/* ── 按鈕 ── */
.nav-btn {
    width: 44px;
    height: 44px;
    min-width: 44px;
    background: transparent;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0;
    padding: 0;
    color: var(--muted);
    white-space: nowrap;
    overflow: hidden;
    transition: background 0.15s, color 0.15s,
                width 0.25s cubic-bezier(0.4, 0, 0.2, 1),
                gap 0.25s, padding 0.25s;
}
#sidebar.expanded .nav-btn:not(#sidebar-toggle) {
    width: 100%;
    justify-content: flex-start;
    gap: 10px;
    padding: 0 10px;
}
#sidebar-toggle {
    flex-shrink: 0;
    margin-left: auto;
}
@media (hover: hover) and (pointer: fine) {
    .nav-btn:hover {
        background: var(--accent-bg);
        color: var(--text);
    }
}
.nav-btn.nav-active {
    background: var(--accent-bg);
    color: var(--ink);
    font-weight: 500;
}

/* ── 圖示 ── */
.nav-icon {
    font-size: 1.3rem;
    flex-shrink: 0;
    width: 24px;
    text-align: center;
    line-height: 1;
}

/* ── 文字標籤（收納時隱藏） ── */
.nav-label {
    font-size: 0.88rem;
    font-weight: 500;
    opacity: 0;
    width: 0;
    overflow: hidden;
    pointer-events: none;
    transition: opacity 0.15s 0s, width 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}
#sidebar.expanded .nav-label {
    opacity: 1;
    width: auto;
    transition: opacity 0.2s 0.1s, width 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ════════════════════════════════════════
   深色模式 — 側欄
   ════════════════════════════════════════ */
html[data-theme="dark"] #sidebar {
    background: var(--surface);
    border-right-color: var(--accent-bg);
}
html[data-theme="dark"] .nav-btn {
    color: var(--muted);
}
html[data-theme="dark"] .nav-btn.nav-active {
    background: var(--accent-bg);
    color: var(--ink);
}
html[data-theme="dark"] .nav-divider {
    background: var(--accent-bg);
}
html[data-theme="dark"] #sidebar-title {
    color: var(--ink);
}