> dug into it and thought about what was missing

Got bitten by it. A fixed input at the top of the screen just disappeared. Needed an entry in the page meta to sort it.

That's a good, concrete example. This is the blind spot of preview tools. These are the kinds of bugs — viewport behavior with keyboard input, 100vh glitches — that the preview won't show at all because there's no keyboard. Now if i go for keyboard/viewport simulation, I'll know where to start looking and what will help me fix them (interactive-widget=resizes-content, etc.).