The model will happily produce the interface it has seen the most: purple-on-black, three feature cards, “Welcome to your app.” That is not a surprise. It is the prior.
You change the prior with files.
Write the forbidden list
“Make it beautiful” is not a constraint. “Do not use rainbow borders. One accent. Buttons start with a verb.” is. The UI craft and product copy rules on this site are that list, scoped so they do not nag a migration.
Audit before you restyle everything
The anti-slop skill scores screens, then rewrites the worst three. A whole-app theme pass is how you invent a second design system by accident.
Empty, loading, error
A generated UI is often a happy path with a spinner. If a list can be empty, say what is missing and the next action. If a pack download fails, say “Pack download failed,” not “Something went wrong.”
Test it
New chat: “Add a settings page.” If the result still looks like a template, the rule is too long, always-on among too many others, or written as inspiration.