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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: #333;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
}

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

header {
    background: white;
    border-radius: 15px;
    padding: 20px;
    margin-bottom: 20px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
    text-align: center;
}

header h1 {
    color: #4a5568;
    margin-bottom: 10px;
}

.score-display {
    background: #48bb78;
    color: white;
    padding: 10px 20px;
    border-radius: 25px;
    font-weight: bold;
    display: inline-block;
}

main {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
}

section {
    background: white;
    border-radius: 15px;
    padding: 25px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
}

.lesson-section {
    grid-column: 1 / -1;
}

.quiz-section, .exercise-section {
    min-height: 400px;
}

h2 {
    color: #4a5568;
    border-bottom: 3px solid #667eea;
    padding-bottom: 10px;
    margin-bottom: 20px;
}

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

.lesson-text {
    margin-bottom: 20px;
    font-size: 16px;
}

.lesson-image {
    max-width: 100%;
    height: auto;
    border-radius: 10px;
    margin: 15px 0;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.question {
    margin-bottom: 25px;
    padding: 15px;
    background: #f7fafc;
    border-radius: 10px;
    border-left: 4px solid #667eea;
}

.question-text {
    font-weight: 600;
    margin-bottom: 15px;
    color: #2d3748;
}

.options {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.option-label {
    display: flex;
    align-items: center;
    padding: 10px;
    background: white;
    border: 2px solid #e2e8f0;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s ease;
}

.option-label:hover {
    border-color: #667eea;
    background: #f0f4ff;
}

.option-label input {
    margin-right: 10px;
}

.exercise-question {
    margin-bottom: 20px;
    font-weight: 600;
    color: #2d3748;
}

textarea {
    width: 100%;
    padding: 15px;
    border: 2px solid #e2e8f0;
    border-radius: 10px;
    font-family: inherit;
    font-size: 14px;
    resize: vertical;
    transition: border-color 0.3s ease;
}

textarea:focus {
    outline: none;
    border-color: #667eea;
}

button {
    background: #667eea;
    color: white;
    border: none;
    padding: 12px 30px;
    border-radius: 25px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    margin-top: 15px;
}

button:hover {
    background: #5a67d8;
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(102, 126, 234, 0.4);
}

.feedback {
    margin-top: 20px;
    padding: 15px;
    border-radius: 10px;
    text-align: center;
    font-weight: 600;
}

.feedback.success {
    background: #c6f6d5;
    color: #22543d;
    border: 2px solid #48bb78;
}

.feedback.warning {
    background: #fed7d7;
    color: #742a2a;
    border: 2px solid #f56565;
}

.hint {
    background: #fffaf0;
    border: 2px solid #ed8936;
    border-radius: 8px;
    padding: 10px;
    margin: 10px 0;
    font-size: 14px;
    color: #744210;
}

@media (max-width: 768px) {
    main {
        grid-template-columns: 1fr;
    }
    
    .container {
        padding: 10px;
    }
    
    section {
        padding: 15px;
    }
}