* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: black;
}

.cube {
    position: relative;
    width: 300px;
    height: 300px;
    transform-style: preserve-3d;
    transform: rotateX(-30deg);
    animation: animate 4s linear infinite;
}

@keyframes animate {
    0% {
        transform: rotateX(-30deg) rotateY(0deg);
    }
    100% {
        transform: rotateX(-30deg) rotateY(360deg);
    }
}

.cube div {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    transform-style: preserve-3d;
}

.cube div span {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(blue, red);
    transform: rotateY(calc(90deg * var(--side))) translateZ(10px);
}