How can one create an overlay in css?

Question

I\'d like to create a div with an arbitrary size, then display something on top of that div. What is the best way to position and size the overlay exactly as the div below i

Answer 1

http://jsfiddle.net/55LNG/1/

CSS:

#box{
    border:1px solid black;
    position:relative;
}
#overlay{
    position:absolute;
    top:0px;
    left:0px;
    bottom:0px;
    right:0px;
    background-color:rgba(255,255,0,0.5);
}