.display-6 {
    animation: pulse 2s infinite;
}
@keyframes pulse {
    0% { opacity: 0.8; }
    50% { opacity: 1; }
    100% { opacity: 0.8; }
}

.spacer { height: 100vh; display: flex; align-items: center; justify-content: center; color: #888; }
.box { 
    width: 200px; height: 200px; background-color: #cc0000; 
    margin: 100px auto; opacity: 0; /* Hidden by default */
}