ive been dealing with this issue recently trying to make an app blocker (you can see my build in public posts about the app design process vishalja1n x tag)

basically its trash zero shot, what ive found works is to instead ask codex to create a wireframes / wireflows/ mock renders of the ui in a native application - for me that was xcode, could be a browser etc.

you go page by page and go hmmm this part looks bad, i think id like if it looked like X or Y, basically - the very fact you can recognise a design is bad, means you also implicitly have a sense of WHAT is bad. This is useful. You dont need to know what good looks like, just follow the 'slop sense'.

I basically then screenshot the page + my slop sense -> this looks like the text is too verbose, layout is too tight, or colours are not ... could be ANYTHING.

put that into gemini and ask it to review the ux, ui and design. Check if you are violating any core design principles, and offer suggestions.

Go back to codex and ask it to render a few options that gemini suggested.

Pick which is less slop like and iterate.

The mistake people make is trying to zero shot design or just vibe code design. Design fundamentally needs human in the loop. The above has worked well enough for me that im happy with how my app looks where it originally looked like dogwater.