:root {
    --primary-color: #4a6fa5;
    --secondary-color: #6b8cbc;
    --success-color: #4caf50;
    --error-color: #f44336;
    --warning-color: #ff9800;
    --light-color: #f5f5f5;
    --dark-color: #333;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --border-radius: 8px;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    background-color: #f0f2f5;
    color: var(--dark-color);
    line-height: 1.6;
}

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

header {
    text-align: center;
    margin-bottom: 30px;
    padding: 20px;
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

h1 {
    color: var(--primary-color);
    margin-bottom: 10px;
}

.upload-section {
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 20px;
    margin-bottom: 20px;
}

.file-selection {
    margin-bottom: 15px;
}

.file-select {
    width: 100%;
    padding: 12px 15px;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
    margin-bottom: 10px;
    background-color: white;
}

.upload-area {
    border: 2px dashed #ddd;
    border-radius: var(--border-radius);
    padding: 15px;
    text-align: center;
    margin-bottom: 15px;
    transition: all 0.3s;
    cursor: pointer;
}

.upload-area:hover {
    border-color: var(--primary-color);
    background-color: rgba(74, 111, 165, 0.05);
}

.upload-area.highlight {
    border-color: var(--primary-color);
    background-color: rgba(74, 111, 165, 0.1);
}

.upload-icon {
    font-size: 1.5rem;
    color: var(--primary-color);
    margin-bottom: 5px;
}

.file-input {
    display: none;
}

.upload-btn {
    background-color: var(--primary-color);
    color: white;
    padding: 8px 16px;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 0.9rem;
    transition: background-color 0.3s;
    margin-top: 5px;
}

.upload-btn:hover {
    background-color: var(--secondary-color);
}

.progress-container {
    margin: 20px 0;
    background-color: #e0e0e0;
    border-radius: 10px;
    height: 10px;
    overflow: hidden;
}

.progress-bar {
    height: 100%;
    background-color: var(--primary-color);
    width: 0%;
    transition: width 0.3s ease;
}

.stats {
    display: flex;
    justify-content: space-between;
    margin-bottom: 20px;
    font-size: 0.9rem;
    color: #666;
}

.card {
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 25px;
    margin-bottom: 20px;
    transition: transform 0.3s ease;
}

.card:hover {
    transform: translateY(-5px);
}

.question {
    font-size: 1.5rem;
    margin-bottom: 20px;
    text-align: center;
    font-weight: 600;
}

.position-info {
    text-align: center;
    margin-bottom: 15px;
    color: #666;
    font-size: 0.9rem;
}

.answer-input {
    width: 100%;
    padding: 12px 15px;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
    margin-bottom: 15px;
    transition: border-color 0.3s;
}

.answer-input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.buttons {
    display: flex;
    gap: 10px;
    margin-bottom: 15px;
}

button {
    padding: 10px 15px;
    border: none;
    border-radius: var(--border-radius);
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s;
    flex: 1;
}

.check-btn {
    background-color: var(--primary-color);
    color: white;
}

.check-btn:hover {
    background-color: var(--secondary-color);
}

.skip-btn {
    background-color: #e0e0e0;
    color: var(--dark-color);
}

.skip-btn:hover {
    background-color: #d0d0d0;
}

.next-btn {
    background-color: var(--success-color);
    color: white;
    margin-top: 10px;
}

.next-btn:hover {
    background-color: #45a049;
}

.feedback {
    padding: 15px;
    border-radius: var(--border-radius);
    margin-top: 15px;
    display: none;
}

.correct {
    background-color: rgba(76, 175, 80, 0.1);
    border-left: 4px solid var(--success-color);
    color: var(--success-color);
}

.incorrect {
    background-color: rgba(244, 67, 54, 0.1);
    border-left: 4px solid var(--error-color);
    color: var(--error-color);
}

.correct-answer {
    font-weight: bold;
    margin-top: 10px;
}

.next-hint {
    margin-top: 10px;
    font-style: italic;
    color: #666;
}

.controls {
    display: flex;
    justify-content: space-between;
    margin-top: 20px;
}

.control-btn {
    background-color: var(--light-color);
    color: var(--dark-color);
    padding: 8px 15px;
    border-radius: var(--border-radius);
    border: 1px solid #ddd;
    cursor: pointer;
    transition: all 0.3s;
}

.control-btn:hover {
    background-color: #e0e0e0;
}

.difficulty-selector {
    display: flex;
    gap: 10px;
    margin-bottom: 20px;
}

.difficulty-btn {
    flex: 1;
    padding: 8px;
    text-align: center;
    background-color: var(--light-color);
    border: 1px solid #ddd;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: all 0.3s;
}

.difficulty-btn.active {
    background-color: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

.difficulty-btn.disabled {
    opacity: 0.5;
    cursor: not-allowed;
    background-color: #f5f5f5;
}

.completion-message {
    text-align: center;
    padding: 30px;
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    margin-bottom: 20px;
}

.completion-message h2 {
    color: var(--success-color);
    margin-bottom: 15px;
}

.history {
    margin-top: 30px;
}

.history-item {
    padding: 10px;
    border-bottom: 1px solid #eee;
    display: flex;
    justify-content: space-between;
}

.history-item:last-child {
    border-bottom: none;
}

.status-correct {
    color: var(--success-color);
}

.status-incorrect {
    color: var(--error-color);
}

.status-skipped {
    color: var(--warning-color);
}

.hidden {
    display: none;
}

@media (max-width: 600px) {
    .container {
        padding: 10px;
    }
    
    .question {
        font-size: 1.2rem;
    }
    
    .buttons {
        flex-direction: column;
    }
}