:root {
    --primary-color: #333333;
    --secondary-color: #666666;
    --accent-color: #007AFF; /* iOS Blue style for links/accents if needed */
    --bg-color: #F5F5F7;
    --card-bg: #FFFFFF;
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
    --spacing-unit: 16px;
}

/* Top scroll progress */
.scroll-progress {
    position: fixed;
    top: 0;
    left: 0;
    height: 3px;
    width: 0;
    background-color: var(--accent-color);
    z-index: 9999;
    transition: width 0.1s linear;
}

/* Back to Top Button */
.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 44px;
    height: 44px;
    background-color: var(--card-bg);
    color: var(--accent-color);
    border: 1px solid rgba(0,0,0,0.1);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: all 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
    z-index: 999;
    outline: none;
    -webkit-tap-highlight-color: transparent;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.back-to-top:active {
    transform: scale(0.95);
    background-color: #f0f0f0;
}

.back-to-top svg {
    width: 20px;
    height: 20px;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--primary-color);
    line-height: 1.6;
    font-size: 14px; /* Base size for mobile */
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.container {
    max-width: 600px; /* Limit width on tablets/desktop */
    margin: 0 auto;
    background-color: var(--card-bg);
    min-height: 100vh;
    padding: 24px 20px 40px;
    box-shadow: 0 0 20px rgba(0,0,0,0.02);
}

/* Header */
header {
    text-align: center;
    margin-bottom: 32px;
    padding-bottom: 16px;
    border-bottom: 1px solid #EEEEEE;
}

h1 {
    font-size: 20px;
    font-weight: 600;
    color: #000;
    margin-bottom: 8px;
}

.update-time {
    font-size: 12px;
    color: #999;
}

/* Content Hierarchy */

/* Level 1: Main Sections */
.section {
    margin-bottom: 32px;
}

.level-1-title {
    font-size: 17px;
    font-weight: 600;
    color: #000;
    margin-bottom: 16px;
    position: relative;
    padding-left: 12px;
}

.level-1-title::before {
    content: '';
    position: absolute;
    left: 0;
    top: 4px;
    bottom: 4px;
    width: 4px;
    background-color: var(--accent-color);
    border-radius: 2px;
}

/* Level 2: Sub-sections */
.sub-section {
    margin-bottom: 20px;
    padding-left: 4px;
}

.level-2-title {
    font-size: 15px;
    font-weight: 600;
    color: #222;
    margin-bottom: 10px;
}

/* Level 3: Details */
.detail-item {
    margin-bottom: 12px;
    padding-left: 0; /* Keep aligned left for mobile readability */
}

.level-3-title {
    font-size: 14px;
    font-weight: 500; /* Slightly less bold than headers */
    color: #333;
    margin-bottom: 6px;
    display: inline-block; /* Inline with text usually, or block depending on style */
}

p {
    font-size: 14px;
    color: var(--secondary-color);
    margin-bottom: 12px;
    text-align: justify;
}

strong {
    font-weight: 700;
    color: #000; /* Ensure strong text is darker */
}

ul {
    padding-left: 20px;
    margin-bottom: 12px;
}

li {
    font-size: 14px;
    color: var(--secondary-color);
    margin-bottom: 6px;
}

/* Footer */
footer {
    margin-top: 40px;
    text-align: center;
    font-size: 12px;
    color: #999;
    padding-top: 20px;
    border-top: 1px dashed #EEE;
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
    :root {
        --primary-color: #E0E0E0;
        --secondary-color: #A0A0A0;
        --bg-color: #000000;
        --card-bg: #1C1C1E;
        --accent-color: #0A84FF;
    }

    header {
        border-bottom-color: #333;
    }

    h1, .level-1-title, h3, .level-2-title, strong {
        color: #FFF;
    }
    
    .level-3-title {
        color: #ddd;
    }

    footer {
        border-top-color: #333;
    }

    .back-to-top {
        background-color: #2C2C2E;
        border-color: rgba(255,255,255,0.1);
    }
    
    .back-to-top:active {
        background-color: #3a3a3c;
    }
}