loading overlay demo

HTML

<link rel="stylesheet" href="//netdna.bootstrapcdn.com/font-awesome/4.0.3/css/font-awesome.css">
<section>
    <div id="overlay"> 
        <i class="fa fa-spinner fa-spin spin-big"></i>
    </div>
</section>

<section>
    <div id="overlay"> 
        <i class="fa fa-spinner fa-spin spin-normal"></i>
    </div>
</section>

<section>
    <div id="overlay"> 
        <i class="fa fa-spinner fa-spin spin-small"></i>
    </div>
</section>

CSS

section {
    width: 200px;
    height: 200px;
    margin: 50px;
}
#overlay {
    position: relative;
    width: 100%;
    height: 100%;
    z-index: 99999999999;
    background: rgba(0, 0, 0, 0.5);
}
#overlay i {
    position: absolute;
    top: 50%;
    left: 50%;
}
.spin-big {
    font-size: 50px;
    height: 50px;
    width: 50px;
    margin-top: -25px;
    margin-left: -25px;
}
.spin-normal {
    font-size: 35px;
    height: 35px;
    width: 35px;
    margin-top: -22.5px;
    margin-left: -22.5px;
}
.spin-small {
    font-size: 20px;
    height: 20px;
    width: 20px;
    margin-top: -10px;
    margin-left: -10px;
}