CSS
Stacking context
A layering scope created by position with z-index, transform, opacity below 1, or filter.
Why interviewers ask about it
Why z-index: 9999 sometimes does nothing - the element is trapped inside a context its ancestor created. An opacity of 0.99 is enough to create one.
Related terms
This term is part of the free Python Full-Stack interview preparation module - browse the full glossary for every definition.