body {
    gap: 40px;
}

.corner {
    position: relative;
    width: 150px;
    height: 150px;
    background: rgba(34, 34, 34,1);
    overflow: hidden;
    transform: rotate(calc(90deg * var(--i)));
}

.corner::before {
    content: '';
    position: absolute;
    width: 300px;
    height: 300px;
    background: radial-gradient(var(--clr), transparent, transparent);
    animation: animate 1.5s linear infinite;
}
.corner::after {
    content: '';
    position: absolute;
    inset: 2px;
    background: rgba(34, 34, 34,0.9);
}

@keyframes animate{
    0% {
        transform: translate(-150px, -150px);
    }
    25% {
        transform: translate(0px, -150px);
    }
    50% {
        transform: translate(0px, 0px);
    }
    75% {
        transform: translate(-150px, 0px);
    }
    100% {
        transform: translate(-150px, -150px);
    }
}