You added broken link. In general if you put div2 inside div1 - div2 have 0px height (is empty!!) so most of the time the trick of overlay involved with some trick that stretch this div (the “empty” div2). otherwise you dont see any bg color or effect.
Example:
https://stackoverflow.com/questions/2941189/how-to-overlay-one-div-over-another-div
Again add link or example for better answer. You can solve a lot of this issues by :hover (without any extra div or markup).
Also in webflow templates you find a lot of overlay divs ideas. Try to learn the structure.