Tunnel animation

by rulokc

HTML

<div class="container">
    <div class="circle"></div>
</div>

CSS

.container {
    background-color: #00f;
    width: 200px;
    height: 200px;
    display: flex;
}
.circle {
    width: 0;
    height: 0;
    border: 1px solid #fff;
    margin: auto;
    -webkit-animation: grow 1s linear infinite;
}
@-webkit-keyframes grow {
    from {
        width: 0;
        height: 0;
    }
    to {
        width: 100%;
        height: 100%;
    }
}