* {
    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;
    justify-content: center;
    align-items: center;
    color: #333;
}

.container {
    text-align: center;
    padding: 20px;
    max-width: 600px;
    width: 100%;
}

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

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

.card {
    width: 100%;
    height: 300px;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.6s;
    cursor: pointer;
}

.card.is-flipped {
    transform: rotateY(180deg);
}

.card-front,
.card-back {
    width: 100%;
    height: 100%;
    position: absolute;
    backface-visibility: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    border-radius: 15px;
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.3);
    padding: 30px;
}

.card-front {
    background-color: #fff;
    color: #333;
}

.card-back {
    background-color: #4CAF50;
    color: white;
    transform: rotateY(180deg);
}

.card-front p,
.card-back p {
    font-size: 1.5em;
    line-height: 1.6;
}

.controls {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 20px;
}

button {
    background-color: white;
    color: #667eea;
    border: none;
    padding: 12px 24px;
    font-size: 1em;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
}

button:hover {
    background-color: #f0f0f0;
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.3);
}

button:active {
    transform: translateY(0);
}

button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

#progress {
    color: white;
    font-size: 1.2em;
    font-weight: bold;
    min-width: 80px;
    text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.3);
}