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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: #333;
    background: linear-gradient(135deg, #f5d020 0%, #f53803 100%);
    min-height: 100vh;
    padding-bottom: 2rem;
}

header {
    background: linear-gradient(135deg, #f5d020 0%, #f53803 100%);
    color: white;
    text-align: center;
    padding: 3rem 1rem;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

header h1 {
    font-size: clamp(2rem, 5vw, 3.5rem);
    margin-bottom: 0.5rem;
    font-weight: 800;
}

.subtitle {
    font-size: clamp(1rem, 3vw, 1.25rem);
    opacity: 0.95;
    font-weight: 500;
}

.container {
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 1rem;
}

.intro {
    background: white;
    border-radius: 16px;
    padding: 2rem;
    margin-bottom: 3rem;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.intro h2 {
    color: #f53803;
    margin-bottom: 1rem;
    font-size: clamp(1.5rem, 4vw, 2rem);
}

.intro p {
    font-size: 1.1rem;
    color: #555;
}

.part {
    margin-bottom: 3rem;
}

.part > h2 {
    color: white;
    font-size: clamp(1.5rem, 4vw, 2rem);
    margin-bottom: 1.5rem;
    padding: 0 0.5rem;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

.lesson-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
}

.lesson-card {
    background: white;
    border-radius: 12px;
    padding: 1.5rem;
    text-decoration: none;
    color: #333;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.lesson-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    background: linear-gradient(135deg, #f5d020 0%, #f53803 100%);
    transform: scaleY(0);
    transition: transform 0.3s ease;
}

.lesson-card:hover::before {
    transform: scaleY(1);
}

.lesson-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
}

.lesson-number {
    display: inline-block;
    background: linear-gradient(135deg, #f5d020 0%, #f53803 100%);
    color: white;
    font-weight: 800;
    font-size: 0.875rem;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    margin-bottom: 0.75rem;
}

.lesson-card h3 {
    font-size: 1.25rem;
    margin-bottom: 0.5rem;
    color: #f53803;
}

.lesson-card p {
    color: #666;
    font-size: 0.95rem;
}

.code-block {
    background: #1e1e1e;
    border-radius: 8px;
    padding: 1.5rem;
    margin: 1rem 0;
    overflow-x: auto;
}

.code-block pre {
    margin: 0;
    white-space: pre-wrap;
    word-wrap: break-word;
}

.code-block code {
    color: #d4d4d4;
    font-family: 'Courier New', monospace;
    font-size: 0.9rem;
    line-height: 1.5;
    display: block;
    white-space: pre-wrap;
}

section {
    margin-bottom: 3rem;
}

section h2 {
    color: #f53803;
    margin-bottom: 1rem;
    font-size: clamp(1.5rem, 4vw, 2rem);
}

section h3 {
    color: #f5d020;
    margin: 1.5rem 0 0.75rem;
    font-size: 1.25rem;
}

section p {
    margin-bottom: 1rem;
    color: #333;
}

section ul, section ol {
    margin: 1rem 0;
    padding-left: 2rem;
}

section li {
    margin-bottom: 0.5rem;
    color: #333;
}

.key-points {
    background: linear-gradient(135deg, rgba(245, 208, 32, 0.1) 0%, rgba(245, 56, 3, 0.1) 100%);
    border-left: 4px solid #f53803;
    padding: 1.5rem;
    border-radius: 8px;
    list-style: none;
}

.key-points li {
    padding: 0.5rem 0;
    position: relative;
    padding-left: 1.5rem;
}

.key-points li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: #f53803;
    font-weight: bold;
}

.key-points strong {
    color: #f53803;
}

.page-nav {
    display: flex;
    justify-content: space-between;
    gap: 1rem;
    margin-top: 3rem;
    padding-top: 2rem;
    border-top: 2px solid #eee;
}

.page-nav a {
    padding: 0.75rem 1.5rem;
    background: linear-gradient(135deg, #f5d020 0%, #f53803 100%);
    color: white;
    text-decoration: none;
    border-radius: 8px;
    font-weight: 600;
    transition: all 0.3s ease;
}

.page-nav a:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(245, 56, 3, 0.3);
}

footer {
    text-align: center;
    color: white;
    padding: 2rem 1rem;
    margin-top: 3rem;
    text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.2);
}

@media (max-width: 768px) {
    .lesson-grid {
        grid-template-columns: 1fr;
    }
    
    .page-nav {
        flex-direction: column;
    }
}