"Pixel perfect" is about attention to detail and consistency. Margins, padding, or the combination of these inside other containers will stick out when they're not consistent.
Here's an example that I personally encountered: what if you have a <h1>Text</h1> and it has a certain left margin.
Then another heading except it has a nested button component (which internally comes with some padding). Then the "Text" in both aren't aligned from section to section and it is jarring.
Now that Cursor has moved towards a credits system, grok code fast is making the plan last while still being reasonable in inference time. GPT 5 and GPT 5 Codex actually moves my "amount remaining" bar in realtime while being incredibly slow.
Here's an example that I personally encountered: what if you have a <h1>Text</h1> and it has a certain left margin. Then another heading except it has a nested button component (which internally comes with some padding). Then the "Text" in both aren't aligned from section to section and it is jarring.