html

<div class="loading"><div class="loading-wheel"></div></div>

Loading overlay

.loading {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: 99999;
    background-color: rgba(0,0,0,.4);
}

.loading-wheel {
    width: 20px;
    height: 20px;
    margin-top: -40px;
    margin-left: -40px;
    position: absolute;
    top: 50%;
    left: 50%;
    border-width: 30px;
    border-radius: 50%;
    -webkit-animation: spin 1s linear infinite;
    border-style: double;
    border-color: #ccc transparent;
}

@-webkit-keyframes spin {
    0% {
        -webkit-transform: rotate(0);
    }
    100% {
        -webkit-transform: rotate(-360deg);
    }
}