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

Quick answer without seeing examples of your current HTML and CSS is to use z-index

css:

#div1 {
position: relative;
z-index: 1;
}

#div2 {
position: relative;
z-index: 2;
}

Where div2 is the overlay