”z-index: 10000” is a solution employed by people who have no idea what a stacking context is, and, consequently, do not know that one can define their own ”top layer” and have z-indexes inside that work completely separate from the rest of the document.

Just set ”position: relative” on an element and it will start a new stacking context, and stack it within the underlying context. It’s like having a card in a card stack be another stack of cards.