body {
    height: 100vh;
}
#challenge17 {
    display: flex;
    align-items: center;
    justify-content: center;
}

#challenge17 .loading {
    position: relative;
    width: 150px;
    height: 150px;
    border-radius: 10px;
    background-color: #0099eb;
    box-shadow: 0 1px 10px rgba(0, 0, 0, 0.315);
    animation: loading-square 10s linear infinite;
}

@keyframes loading-square {
    0% { 
        transform: rotateX(0) rotateY(0deg);
    }
    50% {
        transform: rotateX(0) rotateY(-180deg);
    }
    100% {
        transform: rotateX(180deg) rotateY(-180deg);
    }
}