Dynamic elements
Reload this page and the id below changes every time, so code that hard-codes it will break. The two buttons stay in their initial state until client-side JS updates them a few seconds later, so a plain HTTP fetch (no JS execution) will never see their final state.
Randomized id
This paragraph's id is random-text-be8364b2 on this request; it'll be different on the next one. Select it by the stable data-testid="random-text" attribute instead.