/* General styles */
body {
    font-family: Arial, sans-serif;
    max-width: 210mm;
    margin: 0 auto;
    padding: 20px;
    background: white;
    line-height: 1.6;
}

.main-content {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.header {
    text-align: center;
    margin-bottom: 30px;
    position: relative;
}

.back-button {
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
}

.back-link {
    color: #4a90e2;
    text-decoration: none;
    font-size: 16px;
    display: flex;
    align-items: center;
    padding: 8px 12px;
    border-radius: 5px;
    transition: background-color 0.2s;
}

.back-link:hover {
    background-color: #f0f7ff;
}

h1 {
    color: #4a90e2;
    font-size: 2.5em;
    margin: 0;
}

/* Lesson sections */
.lesson-section {
    margin-bottom: 40px;
    background: #fff;
    border-radius: 8px;
    padding: 30px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

h2 {
    color: #4a90e2;
    font-size: 1.8em;
    margin: 0 0 20px 0;
}

/* Symbol grid */
.symbol-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(100px, 1fr));
    gap: 20px;
    margin: 20px 0;
}

.symbol-item {
    background: #f0f7ff;
    border-radius: 8px;
    padding: 20px;
    text-align: center;
    transition: transform 0.2s;
}

.symbol-item:hover {
    transform: scale(1.05);
}

.symbol {
    font-size: 2.5em;
    font-weight: bold;
    color: #4a90e2;
    font-family: "Times New Roman", Times, serif;
}

.value {
    font-size: 1.2em;
    color: #666;
    margin-top: 5px;
}

/* Rule boxes */
.rule-box {
    background: #f8f9fa;
    border-radius: 8px;
    padding: 20px;
    margin-bottom: 30px;
}

.rule-box h3 {
    color: #4a90e2;
    margin: 0 0 15px 0;
    font-size: 1.4em;
}

.examples-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 15px;
    margin: 20px 0;
}

.example {
    background: white;
    padding: 10px;
    border-radius: 4px;
    text-align: center;
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
    font-family: "Times New Roman", Times, serif;
    font-size: 1.2em;
}

.rules-list {
    margin: 0;
    padding-left: 20px;
}

.rules-list li {
    margin-bottom: 10px;
    color: #444;
}

/* Practice section */
.practice-section {
    text-align: center;
    margin-top: 40px;
    padding: 30px;
    background: #f0f7ff;
    border-radius: 8px;
}

.practice-links {
    display: flex;
    justify-content: center;
    gap: 20px;
    margin-top: 20px;
    flex-wrap: wrap;
}

.practice-link {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 15px 25px;
    background: #4a90e2;
    color: white;
    text-decoration: none;
    border-radius: 8px;
    transition: background-color 0.2s;
}

.practice-link:hover {
    background: #357abd;
}

.arrow {
    font-size: 1.2em;
}

/* Responsive styles */
@media (max-width: 600px) {
    .header {
        padding-top: 40px;
    }
    
    .back-button {
        top: 0;
        left: 50%;
        transform: translateX(-50%);
    }
    
    h1 {
        font-size: 2em;
    }

    .lesson-section {
        padding: 20px;
    }

    .symbol-grid {
        grid-template-columns: repeat(auto-fit, minmax(80px, 1fr));
    }

    .practice-links {
        flex-direction: column;
    }

    .practice-link {
        width: