.fade-in {
    animation: fadeIn 0.4s;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.flip {
    animation: flip 0.5s;
}

@keyframes flip {
    to { transform: rotateY(360deg); }
}

.correct {
    background: #2ecc71 !important;
}

.wrong {
    background: #e74c3c !important;
}