@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); border-color: #ef4444; /* red-500 */ }
    75% { transform: translateX(5px); border-color: #ef4444; }
}

.shake-animation {
    animation: shake 0.4s ease-in-out;
}