@keyframes shake {
    0%, 100% { transform: translateX(0); }
    20%, 60% { transform: translateX(-5px); }
    40%, 80% { transform: translateX(5px); }
}

.shake {
    animation: shake 0.3s ease-in-out;
}

.alert-message {
    color: #fff;
    background-color: #e74c3c;
    padding: 10px;
    border-radius: 5px;
    margin-top: 10px;
    display: none;
    text-align: center;
    font-size: 0.9em;
}