:root {
    --primary-color: #2c3e50;
    --accent-color: #e67e22;
    --bg-color: #f4f7f6;
    --card-front-bg: #ffffff;
    --card-back-bg: #fdfaf5;
    --text-color: #333;
    --shadow: 0 4px 15px rgba(0,0,0,0.1);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    padding: 20px;
}

header {
    text-align: center;
    margin-bottom: 40px;
    display: flex;
    justify-content: center;
}

.header-content {
    display: flex;
    align-items: center;
    gap: 30px;
    max-width: 800px;
    text-align: left;
}

.book-cover {
    width: 120px;
    height: auto;
    border-radius: 8px;
    box-shadow: var(--shadow);
}

header h1 {
    font-size: 2.2rem;
    color: var(--primary-color);
    margin-bottom: 10px;
}

.subtitle {
    font-size: 1.1rem;
    color: #666;
}

/* 筛选栏样式 */
#filters {
    max-width: 1200px;
    margin: 0 auto 30px;
    background: white;
    padding: 20px;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.filter-group {
    display: flex;
    align-items: center;
    gap: 15px;
    margin-bottom: 15px;
    border-bottom: 1px solid #eee;
    padding-bottom: 15px;
}

.filter-label {
    font-weight: bold;
    color: var(--primary-color);
}

.filter-btn {
    padding: 8px 16px;
    border: 1px solid #ddd;
    background: white;
    border-radius: 20px;
    cursor: pointer;
    transition: all 0.3s;
    font-size: 0.9rem;
}

.filter-btn:hover {
    background: #f0f0f0;
}

.filter-btn.active {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

.filter-options {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.opt-btn {
    padding: 5px 12px;
    border: none;
    background: #e9ecef;
    border-radius: 15px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: background 0.2s;
}

.opt-btn:hover {
    background: #dee2e6;
}

.opt-btn.selected {
    background: var(--accent-color);
    color: white;
}

/* 卡片容器 */
#card-container {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 30px;
    max-width: 1200px;
    margin: 0 auto;
    padding-bottom: 50px;
}

/* 卡片基础样式 */
.card-wrapper {
    perspective: 1000px;
    height: 420px;
}

.card {
    position: relative;
    width: 100%;
    height: 100%;
    transform-style: preserve-3d;
    -webkit-transform-style: preserve-3d;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    -webkit-transition: -webkit-transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    cursor: pointer;
}

.card.flipped {
    transform: rotateY(180deg);
    -webkit-transform: rotateY(180deg);
}

.card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    border-radius: 15px;
    box-shadow: var(--shadow);
    display: flex;
    flex-direction: column;
    padding: 25px;
    overflow: hidden;
}

/* 卡片正面 */
.card-front {
    background-color: var(--card-front-bg);
    border-top: 5px solid var(--primary-color);
    z-index: 2;
}

.card-chapter {
    font-size: 0.8rem;
    color: var(--accent-color);
    font-weight: bold;
    margin-bottom: 10px;
    text-transform: uppercase;
}

.card-title {
    font-size: 1.25rem;
    font-weight: bold;
    margin-bottom: 20px;
    color: var(--primary-color);
    line-height: 1.3;
}

.card-opinion {
    font-size: 1rem;
    color: #444;
    flex-grow: 1;
    display: flex;
    align-items: center;
    font-style: italic;
}

.card-hint {
    font-size: 0.75rem;
    color: #999;
    text-align: right;
    margin-top: 10px;
}

/* 卡片背面 */
.card-back {
    background-color: var(--card-back-bg);
    transform: rotateY(180deg);
    -webkit-transform: rotateY(180deg);
    border-top: 5px solid var(--accent-color);
}

.card-back h4 {
    font-size: 0.9rem;
    color: var(--accent-color);
    margin-bottom: 15px;
    border-bottom: 1px solid #eee;
    padding-bottom: 5px;
}

.card-quotes {
    font-size: 0.9rem;
    color: #555;
    overflow-y: auto;
    padding-right: 10px;
    flex-grow: 1;
}

.card-quotes p {
    margin-bottom: 15px;
}

.card-themes {
    margin-top: 15px;
    display: flex;
    flex-wrap: wrap;
    gap: 5px;
}

.tag {
    font-size: 0.7rem;
    background: #eee;
    padding: 2px 8px;
    border-radius: 10px;
    color: #777;
}

/* 滚动条美化 */
.card-quotes::-webkit-scrollbar {
    width: 4px;
}

.card-quotes::-webkit-scrollbar-track {
    background: #f1f1f1;
}

.card-quotes::-webkit-scrollbar-thumb {
    background: #ccc;
    border-radius: 10px;
}

.card-quotes::-webkit-scrollbar-thumb:hover {
    background: #999;
}

footer {
    text-align: center;
    margin-top: 40px;
    padding: 20px;
    color: #888;
    font-size: 0.8rem;
}

/* 响应式调整 */
@media (max-width: 600px) {
    .header-content {
        flex-direction: column;
        text-align: center;
        gap: 15px;
    }

    .book-cover {
        width: 100px; /* 移动端缩小封面图，避免占据过多横向空间 */
        margin: 0 auto;
    }

    header h1 {
        font-size: 1.6rem;
    }

    .subtitle {
        font-size: 0.9rem;
    }

    #card-container {
        grid-template-columns: 1fr;
        padding: 0 10px; /* 增加侧边距 */
    }

    .card-wrapper {
        height: 380px; /* 移动端稍微减小卡片高度 */
    }
}