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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: linear-gradient(135deg, #ff6b9d 0%, #c44569 100%);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
    user-select: none;
    -webkit-user-select: none;
    -webkit-tap-highlight-color: transparent;
}

.flash-card {
    width: 90vw;
    height: 80vh;
    max-width: 600px;
    max-height: 800px;
    background: white;
    border-radius: 20px;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.1);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.flash-card:active {
    transform: scale(0.98);
    box-shadow: 0 10px 20px rgba(0, 0, 0, 0.15);
}

.letter {
    font-size: min(25vw, 200px);
    font-weight: 900;
    color: #2c3e50;
    text-align: center;
    line-height: 1;
    transition: all 0.3s ease;
    animation: fadeIn 0.5s ease-out;
}

.capital {
    color: #e84393;
}

.lowercase {
    color: #fd79a8;
}

.instruction {
    position: absolute;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%);
    color: rgba(255, 255, 255, 0.8);
    font-size: 16px;
    text-align: center;
    pointer-events: none;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: scale(0.8);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

@media (max-width: 480px) {
    .flash-card {
        width: 95vw;
        height: 85vh;
        border-radius: 15px;
    }
    
    .letter {
        font-size: 30vw;
    }
    
    .instruction {
        font-size: 14px;
        bottom: 15px;
    }
}

@media (min-width: 768px) {
    .flash-card {
        width: 80vw;
        height: 75vh;
    }
    
    .letter {
        font-size: 20vw;
    }
}