Why might z-index seem to be ignored?
PICTURE THIS: DATABASE INDEX
Simple meaning
Z-index is compared only inside the same stacking context.
WHY — CSS instead of guessing?
Why interviewers care about CSS:
on CSS.
the situation, the default choice, and one exception - that reads as experience.
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:
- 1Z-index is compared only
inside the same stacking context.
- 2Opacity less than one,
transform, filter, or isolation can create a new context so a child cannot escape a parent.
- 3I inspect computed stacking
rather than blindly raising the number to 9999.
- 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
Z-index is compared only inside the same stacking context. Opacity less than one, transform, filter, or isolation can create a new context so a child cannot escape a parent.