:root {
    --bg-day: #fff5e6;
    --text-day: #4e342e;
    --bg-night: #2d2d2d;
    --text-night: #e0e0e0;
    --primary-color: #5d4037; /* 确保变量在外链 CSS 中可用 */
}

body.night-mode {
    background: var(--bg-night) !important;
    color: var(--text-night) !important;
}

.night-mode .chapter-container {
    background: rgba(40, 40, 40, 0.9) !important;
    border-color: #555 !important;
}

#back-to-top {
    position: fixed;
    bottom: 20px;
    right: 20px;
    padding: 10px 15px;
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    opacity: 0;
    transition: opacity 0.3s;
}