:root {
    --bg-color: #ffffff;
    --text-color: #333333;
    --header-bg: #f8f9fa;
    --border-color: #e9ecef;
    --accent-color: #007bff;
    --font-size-base: 16px;
    --line-height: 1.6;
}

[data-theme="dark"] {
    --bg-color: #1a1a1a;
    --text-color: #e0e0e0;
    --header-bg: #2d2d2d;
    --border-color: #404040;
    --accent-color: #4dabf7;
}

* {
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    font-size: var(--font-size-base);
    line-height: var(--line-height);
    color: var(--text-color);
    background-color: var(--bg-color);
    margin: 0;
    padding: 0;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 20px;
}

header {
    background-color: var(--header-bg);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
    transition: background-color 0.3s ease;
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
}

.back-link {
    color: var(--accent-color);
    text-decoration: none;
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.back-link:hover {
    text-decoration: underline;
}

h1 {
    margin: 0;
    font-size: 1.5rem;
    font-weight: 600;
}

.controls {
    display: flex;
    gap: 0.5rem;
    align-items: center;
}

.btn {
    background: var(--accent-color);
    color: white;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 0.25rem;
    cursor: pointer;
    font-size: 0.875rem;
    transition: background-color 0.3s ease;
}

.btn:hover {
    opacity: 0.9;
}

.btn-sm {
    padding: 0.25rem 0.5rem;
    font-size: 0.75rem;
}

nav {
    margin: 2rem 0;
}

.nav-links {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
}

.nav-links a {
    color: var(--accent-color);
    text-decoration: none;
    padding: 0.5rem 0;
    border-bottom: 2px solid transparent;
    transition: border-color 0.3s ease;
}

.nav-links a:hover {
    border-bottom-color: var(--accent-color);
}

main {
    padding: 2rem 0;
}

.post-list {
    list-style: none;
    padding: 0;
    margin: 0;
}

.post-item {
    background: var(--header-bg);
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    transition: background-color 0.3s ease, border-color 0.3s ease;
}

.post {
    background: var(--header-bg);
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    padding: 2rem;
    transition: background-color 0.3s ease, border-color 0.3s ease;
}

.post-title {
    margin: 0 0 0.5rem 0;
    font-size: 1.25rem;
}

.post-title a {
    color: var(--text-color);
    text-decoration: none;
}

.post-title a:hover {
    color: var(--accent-color);
}

.post .post-title {
    margin: 0 0 1rem 0;
    font-size: 2rem;
    line-height: 1.2;
}

.post .post-title a {
    color: var(--text-color);
}

.post-meta {
    font-size: 0.875rem;
    color: var(--text-color);
    opacity: 0.7;
    margin-bottom: 1rem;
}

.post .post-meta {
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border-color);
}

.post-excerpt {
    margin: 0;
    line-height: 1.5;
}

.post-content {
    line-height: 1.8;
}

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

.post-content h2 {
    margin: 2rem 0 1rem 0;
    font-size: 1.5rem;
}

.post-content h3 {
    margin: 1.5rem 0 1rem 0;
    font-size: 1.25rem;
}

.post-content ul {
    margin-bottom: 1.5rem;
    padding-left: 2rem;
}

.post-content li {
    margin-bottom: 0.5rem;
}

.book-info {
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    padding: 1.5rem;
    margin: 2rem 0;
}

.book-title {
    font-style: italic;
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.book-author {
    opacity: 0.8;
    margin-bottom: 1rem;
}

.font-size-controls {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.font-size-display {
    font-size: 0.75rem;
    min-width: 3rem;
    text-align: center;
}

footer {
    background: var(--header-bg);
    border-top: 1px solid var(--border-color);
    padding: 2rem 0;
    margin-top: 3rem;
    text-align: center;
    transition: background-color 0.3s ease, border-color 0.3s ease;
}

@media (max-width: 768px) {
    .container {
        padding: 0 15px;
    }
    
    .header-content {
        flex-direction: column;
        align-items: stretch;
    }
    
    .controls {
        justify-content: center;
    }
    
    h1 {
        text-align: center;
    }
    
    .post-item {
        padding: 1rem;
    }
    
    .post {
        padding: 1.5rem;
    }
    
    .post .post-title {
        font-size: 1.5rem;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 10px;
    }
    
    .nav-links {
        justify-content: center;
    }
    
    .controls {
        flex-wrap: wrap;
        justify-content: center;
    }
}