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

body {
    font-family: 'Arial', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
}

.container {
    width: 100%;
    max-width: 600px;
    text-align: center;
}

h1 {
    color: white;
    margin-bottom: 30px;
    font-size: 2.5rem;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
}

.flashcard-container {
    perspective: 1000px;
    margin-bottom: 30px;
}

.flashcard {
    width: 100%;
    height: 400px;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.6s ease;
    cursor: pointer;
}

.flashcard.flipped {
    transform: rotateY(180deg);
}

.card-front, .card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 15px;
    box-shadow: 0 8px 32px rgba(0,0,0,0.3);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 40px;
}

.card-front {
    background: linear-gradient(135deg, #ffffff 0%, #f8f9fa 100%);
    color: #333;
}

.card-back {
    background: linear-gradient(135deg, #f8f9fa 0%, #e9ecef 100%);
    color: #333;
    transform: rotateY(180deg);
}

.card-front h2 {
    font-size: 2.5rem;
    font-weight: bold;
    text-align: center;
    line-height: 1.2;
}

.info-section {
    margin-bottom: 30px;
    text-align: left;
    width: 100%;
}

.info-section:last-child {
    margin-bottom: 0;
}

.info-section h3 {
    color: #495057;
    font-size: 1.3rem;
    margin-bottom: 10px;
    border-bottom: 2px solid #007bff;
    padding-bottom: 5px;
}

.info-section p {
    font-size: 1.1rem;
    line-height: 1.5;
    color: #666;
}

.controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

button {
    background: linear-gradient(135deg, #007bff 0%, #0056b3 100%);
    color: white;
    border: none;
    padding: 12px 24px;
    border-radius: 25px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 4px 15px rgba(0,123,255,0.3);
}

button:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0,123,255,0.4);
}

button:disabled {
    background: #6c757d;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

#card-counter {
    color: white;
    font-size: 1.1rem;
    font-weight: bold;
    background: rgba(255,255,255,0.2);
    padding: 10px 20px;
    border-radius: 20px;
    backdrop-filter: blur(10px);
}

.progress-bar {
    width: 100%;
    height: 8px;
    background: rgba(255,255,255,0.3);
    border-radius: 10px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, #28a745 0%, #20c997 100%);
    width: 0%;
    transition: width 0.3s ease;
    border-radius: 10px;
}

@media (max-width: 768px) {
    h1 {
        font-size: 2rem;
    }
    
    .flashcard {
        height: 350px;
    }
    
    .card-front h2 {
        font-size: 2rem;
    }
    
    .info-section h3 {
        font-size: 1.1rem;
    }
    
    .info-section p {
        font-size: 1rem;
    }
    
    .controls {
        flex-direction: column;
        gap: 15px;
    }
    
    button {
        width: 100%;
        max-width: 200px;
    }
}