header {
    transition: 1s;
}

.cover-animation {
    animation: cover-animation 20s linear infinite;
}

@keyframes cover-animation {
    0% {
        width: 101%;
        height: 101%;
    }
    80% {
        width: 120%;
        height: 120%;
    }
    100% {
        width: 101%;
        height: 101%;
    }
}