:after pseudo element

by rovision

HTML

<div class="ribbon">
   
</div>

CSS

.ribbon{
    position:relative;
    width:50px;
    height:50px;
    background-color: #3BA8E7;
}
.ribbon:after{
    position:absolute;
    content: " ";
    width:50px;
    height:50px;
    top:20%;
    left:50%;
    background-color: #1578B1;
}