<http://jsfiddle.net/AndyMP/T5pX2/>

```
.block {
    position: relative;
    margin: 25px;
    width: 300px;
    height: 300px;
    border: 1px solid black;
}
.overlay {
    width: 300px;
    height: 300px;
    background: yellow;
    opacity: 0;
}

<div class="block">
    <div class="overlay">
    </div>
</div>

```