What are stacking contexts and how do opacity or transform create them?
PICTURE THIS: DATABASE INDEX
Simple meaning
A stacking context is a local z-index world.
WHY — CSS instead of guessing?
Why interviewers care about CSS:
who only read docs from people who shipped.
and tied to Frontend work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1A stacking context is
a local z-index world.
- 2Transform, opacity less than
one, filter, and isolation create one even at z-index auto.
- 3A child with z-index
999 cannot paint above a sibling of that parent if the parent is a lower context.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
A stacking context is a local z-index world. Transform, opacity less than one, filter, and isolation create one even at z-index auto.