CSS z-index not working (position absolute) [duplicate]

Answer 1

I was struggling to figure it out how to put a div over an image like this:

No matter how I configured z-index in both divs (the image wrapper) and the section I was getting this:

Turns out I hadn't set up the background of the section to be background: white;

so basically it's like this:

  


 


section{
  position: relative;
  background: white; /* THIS IS THE IMPORTANT PART NOT TO FORGET */
}
.img-wrp{
  position: absolute;
  z-index: -1; /* also worked with 0 but just to be sure */
}