I have this div inside another div and I want this div to be the same size as that one but its not scaling up when setting the max-width property.
Link to codepen: https://codepen.io/javas_ninja/pen/zYBaPmr
You didn’t describe your problem properly, since the codepen contains too much code (rather than just the problematic part).
However in general it seems like you might want to set width: 100 %; on the inner div. Max-width is for limiting the maximum size.