/* 기본 리셋 및 공통 스타일 */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Crimson Text', Georgia, serif;
    background-color: #f5f1e9;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    line-height: 1.6;
    color: #2c2c2c;
    padding: 0;
}

/* 레이아웃 */
.content-wrapper {
    display: flex;
    gap: 2rem;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
}

.main-content {
    flex: 1;
    max-width: 800px;
    padding: 1rem;
}

.sidebar {
    width: 320px;
    padding: 2rem;
    background: #fff;
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
    height: fit-content;
    position: sticky;
    top: 2rem;
}

/* 타이포그래피 */
h1 {
    font-size: 2.5rem;
    text-align: center;
    margin-bottom: 3rem;
    color: #1a1a1a;
    font-weight: 700;
    letter-spacing: -0.02em;
}

h2 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    color: #3a3a3a;
}

p {
    font-size: 1.1rem;
    line-height: 1.8;
    color: #4a4a4a;
    margin-bottom: 1.5rem;
}

/* 버튼 스타일 */
.back-button, .next-button, .buy-button {
    display: inline-block;
    padding: 0.8rem 1.5rem;
    background-color: #4a4a4a;
    color: #fff;
    text-decoration: none;
    border-radius: 5px;
    transition: all 0.3s ease;
    font-weight: 500;
}

.back-button:hover, .next-button:hover, .buy-button:hover {
    background-color: #333;
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

/* 책 광고 스타일 */
.book-ad {
    text-align: center;
    padding: 1rem;
    background: #f8f8f8;
    border-radius: 8px;
}

.book-ad img {
    max-width: 220px;
    margin-bottom: 1.2rem;
    border-radius: 8px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.book-ad h3 {
    font-size: 1.2rem;
    margin-bottom: 1rem;
    color: #333;
}

.book-ad p {
    font-size: 0.9rem;
    margin-bottom: 1rem;
    color: #666;
}

/* 네비게이션 버튼 */
.navigation-buttons {
    display: flex;
    justify-content: space-between;
    margin-top: 3rem;
}

/* 반응형 스타일 */
@media (max-width: 1200px) {
    .content-wrapper {
        padding: 0 20px;
    }
}

@media (max-width: 1024px) {
    .content-wrapper {
        flex-direction: column;
        padding: 0.5rem;
        gap: 1.5rem;
    }

    .main-content {
        padding: 0.5rem;
    }

    .sidebar {
        width: 100%;
        position: static;
        margin-top: 2rem;
    }
}

@media (max-width: 768px) {
    body {
        padding: 1rem;
    }

    h1 {
        font-size: 2rem;
        margin-bottom: 2rem;
    }

    h2 {
        font-size: 1.3rem;
    }

    p {
        font-size: 1rem;
    }

    .book-ad img {
        max-width: 180px;
    }
}

@media (max-width: 480px) {
    h1 {
        font-size: 1.8rem;
    }
}

.chapter {
    margin-bottom: 2.5rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid #e0d9d1;
}

.chapter:last-of-type {
    border-bottom: none;
    margin-bottom: 2rem;
}

.chapter-link {
    text-decoration: none;
    display: block;
    transition: transform 0.3s ease;
}

.chapter-link:hover {
    transform: translateX(10px);
}

.chapter-link h2 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    color: #3a3a3a;
}

.chapter-link p {
    font-size: 1.1rem;
    line-height: 1.8;
    color: #4a4a4a;
}

.chapter-link:hover h2 {
    color: #1a1a1a;
}

.lecture-content {
    margin-bottom: 3rem;
}

.lecture-content p {
    margin-bottom: 1.5rem;
}

/* 섹션 스타일 */
.section-title {
    cursor: pointer;
    padding: 1.2rem 1.5rem;
    background: #fff;
    border: 1px solid #e0d9d1;
    border-radius: 8px;
    margin: 1rem 0;
    transition: all 0.3s ease;
    font-size: 1.3rem;
    color: #2c2c2c;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.section-title::after {
    content: '▼';
    font-size: 0.8rem;
    transition: transform 0.3s ease;
}

.section-title.active::after {
    transform: rotate(180deg);
}

.section-title:hover {
    background: #f8f8f8;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
}

.section-content {
    display: none;
    padding: 1.5rem;
    background: #fff;
    margin: 0.5rem 0 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
    border: 1px solid #e0d9d1;
}

@media (max-width: 768px) {
    .section-title {
        padding: 0.9rem 1rem;
        font-size: 1.1rem;
    }

    .section-content {
        padding: 1rem;
    }

    .book-ad img {
        max-width: 180px;
    }
}