:root {
    --primary-color: #3498db;
    --secondary-color: #2ecc71;
    --dark-color: #2c3e50;
    --light-color: #ecf0f1;
    --text-color: #333;
    --border-color: #ddd;
    --shadow: 0 2px 5px rgba(0,0,0,0.1);
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: #f9f9f9;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

header {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: 40px 0;
    text-align: center;
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
}

.subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
}

.main-nav {
    background-color: var(--dark-color);
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

.main-nav ul {
    list-style: none;
    display: flex;
    justify-content: center;
}

.main-nav ul li {
    margin: 0;
}

.main-nav ul li a {
    display: block;
    color: white;
    text-decoration: none;
    padding: 15px 30px;
    transition: background-color 0.3s;
}

.main-nav ul li a:hover,
.main-nav ul li a.active {
    background-color: var(--primary-color);
}

main {
    padding: 40px 0;
}

section {
    margin-bottom: 60px;
}

h2 {
    font-size: 2rem;
    color: var(--dark-color);
    margin-bottom: 30px;
    text-align: center;
}

.hero {
    text-align: center;
    padding: 40px 20px;
    background-color: white;
    border-radius: 8px;
    box-shadow: var(--shadow);
}

.hero p {
    font-size: 1.1rem;
    color: #666;
    max-width: 800px;
    margin: 0 auto;
}

.subject-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
}

.subject-card {
    background-color: white;
    padding: 30px;
    border-radius: 8px;
    box-shadow: var(--shadow);
    text-align: center;
    transition: transform 0.3s, box-shadow 0.3s;
}

.subject-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 15px rgba(0,0,0,0.2);
}

.subject-card h3 {
    color: var(--primary-color);
    margin-bottom: 15px;
    font-size: 1.5rem;
}

.subject-card p {
    color: #666;
    margin-bottom: 20px;
}

.btn {
    display: inline-block;
    background-color: var(--primary-color);
    color: white;
    padding: 10px 25px;
    text-decoration: none;
    border-radius: 5px;
    transition: background-color 0.3s;
}

.btn:hover {
    background-color: #2980b9;
}

.feature-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
}

.feature-item {
    background-color: white;
    padding: 25px;
    border-radius: 8px;
    box-shadow: var(--shadow);
    text-align: center;
}

.feature-item h3 {
    color: var(--secondary-color);
    margin-bottom: 10px;
    font-size: 1.2rem;
}

.feature-item p {
    color: #666;
    font-size: 0.95rem;
}

footer {
    background-color: var(--dark-color);
    color: white;
    text-align: center;
    padding: 20px 0;
    margin-top: 60px;
}

@media (max-width: 768px) {
    header h1 {
        font-size: 2rem;
    }

    .main-nav ul {
        flex-direction: column;
    }

    .main-nav ul li a {
        padding: 10px 20px;
    }

    .subject-grid {
        grid-template-columns: 1fr;
    }

    .formula-section {
        grid-template-columns: 1fr;
    }
}

.formula-section {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 20px;
}

.formula-item {
    background-color: white;
    padding: 25px;
    border-radius: 8px;
    box-shadow: var(--shadow);
    border-left: 4px solid var(--primary-color);
}

.formula-item h3 {
    color: var(--primary-color);
    margin-bottom: 15px;
    font-size: 1.3rem;
}

.formula-item ul {
    list-style: none;
    padding: 0;
}

.formula-item ul li {
    padding: 8px 0;
    border-bottom: 1px solid var(--border-color);
    color: #555;
    font-family: 'Courier New', monospace;
    font-size: 0.95rem;
}

.formula-item ul li:last-child {
    border-bottom: none;
}

.markdown-section {
    background-color: white;
    padding: 40px;
    border-radius: 8px;
    box-shadow: var(--shadow);
}

.markdown-container {
    color: var(--text-color);
    line-height: 1.8;
}

.markdown-container h1 {
    font-size: 2.2rem;
    color: var(--primary-color);
    margin: 30px 0 20px 0;
    padding-bottom: 10px;
    border-bottom: 3px solid var(--primary-color);
}

.markdown-container h2 {
    font-size: 1.8rem;
    color: var(--dark-color);
    margin: 25px 0 15px 0;
    padding-bottom: 8px;
    border-bottom: 2px solid var(--border-color);
}

.markdown-container h3 {
    font-size: 1.5rem;
    color: var(--primary-color);
    margin: 20px 0 12px 0;
}

.markdown-container h4 {
    font-size: 1.3rem;
    color: var(--dark-color);
    margin: 18px 0 10px 0;
}

.markdown-container p {
    margin: 15px 0;
    font-size: 1rem;
}

.markdown-container ul,
.markdown-container ol {
    margin: 15px 0;
    padding-left: 30px;
}

.markdown-container ul li,
.markdown-container ol li {
    margin: 8px 0;
    padding: 5px 0;
}

.markdown-container ul li::marker {
    color: var(--primary-color);
}

.markdown-container ol li::marker {
    color: var(--primary-color);
    font-weight: bold;
}

.markdown-container code {
    background-color: #f4f4f4;
    padding: 2px 6px;
    border-radius: 3px;
    font-family: 'Courier New', monospace;
    font-size: 0.9rem;
    color: #e74c3c;
}

.markdown-container pre {
    background-color: #2c3e50;
    color: #ecf0f1;
    padding: 20px;
    border-radius: 8px;
    overflow-x: auto;
    margin: 20px 0;
}

.markdown-container pre code {
    background-color: transparent;
    color: #ecf0f1;
    padding: 0;
    font-size: 0.9rem;
}

.markdown-container blockquote {
    border-left: 4px solid var(--primary-color);
    margin: 20px 0;
    padding: 10px 20px;
    background-color: #f8f9fa;
    color: #555;
    font-style: italic;
}

.markdown-container a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.3s;
}

.markdown-container a:hover {
    color: var(--secondary-color);
    text-decoration: underline;
}

.markdown-container strong {
    color: var(--dark-color);
    font-weight: 700;
}

.markdown-container em {
    color: #555;
}

.markdown-container hr {
    border: none;
    border-top: 2px solid var(--border-color);
    margin: 30px 0;
}

.markdown-container table {
    width: 100%;
    border-collapse: collapse;
    margin: 20px 0;
    box-shadow: var(--shadow);
}

.markdown-container table th,
.markdown-container table td {
    border: 1px solid var(--border-color);
    padding: 12px 15px;
    text-align: left;
}

.markdown-container table th {
    background-color: var(--primary-color);
    color: white;
    font-weight: 600;
}

.markdown-container table tr:nth-child(even) {
    background-color: #f8f9fa;
}

.markdown-container table tr:hover {
    background-color: #e9ecef;
}

@media (max-width: 768px) {
    .markdown-section {
        padding: 20px;
    }

    .markdown-container h1 {
        font-size: 1.8rem;
    }

    .markdown-container h2 {
        font-size: 1.5rem;
    }

    .markdown-container h3 {
        font-size: 1.3rem;
    }

    .markdown-container table {
        font-size: 0.9rem;
    }

    .markdown-container table th,
    .markdown-container table td {
        padding: 8px 10px;
    }
}