Responsive fluid squares

index.css

/*-- credits: http://jsfiddle.net/josedvq/38Tnx/ --*/

.square-box{
    position: relative;
    width: 50%;
    overflow: hidden;
    background: #4679BD;
}
.square-box:before{
    content: "";
    display: block;
    padding-top: 100%;
}
.square-content{
    position:  absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    color: white;
}
.square-content div {
   display: table;
   width: 100%;
   height: 100%;
}
.square-content span {
    display: table-cell;
    text-align: center;
    vertical-align: middle;
    color: white
}

index.html

<!-- credits: http://jsfiddle.net/josedvq/38Tnx/ -->

<div class='square-box'>
    <div class='square-content'><div><span>Aspect ratio 1:1</span></div></div>
</div>