A side panel slides in when the user opens filters. It is animated by changing `left` from `-320px` to `0`, and on a mid-range Android phone it visibly stutters. Explain what the browser is doing, and what you would change.
Answer it out loud before you open anything. The value of the flags below is in comparing them to what you actually said.
The situation behind the question
A dashboard with a dense results table behind the panel. The animation is smooth on the developer's laptop and on the reviewer's laptop. It was shipped, and support started getting "the filters are laggy" reports from field staff on company-issued phones.
What it is really testing
Whether the candidate can name the pipeline stages a change invalidates, rather than reciting "use transform, it is GPU accelerated". The interesting part is *why* left is expensive here specifically — there is a large table behind the panel — and whether they know what transform gives up in exchange.