<div class="shape-ex1"></div>
.shape-ex1{
    width: 100px;
    height: 100px;
    background-color: #666;
    margin: 0 auto;
    animation: fade 2s linear 0s infinite;
}
@keyframes fade {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.