Design for AIv0, Lovable and Bolt: prompts without a file system
These tools build from a chat box and you rarely touch the files. That changes what a useful prompt looks like: everything has to be in the message, and the message has to fight the tool's house style.
The house style problem
v0 defaults to shadcn components and Tailwind. Lovable defaults to a rounded, soft, gradient-heavy look. Bolt lands somewhere between. None of them is wrong, but if you paste a neo-brutalist card prompt without saying "not the default look", you get a neo-brutalist card with 12px radius and a soft shadow, which is neither.
So the copied prompt for these tools starts with a line that says: plain CSS for these rules, no Tailwind utilities, keep the exact values. It helps. It does not always win. If the result drifts, reply with the single value that is wrong ("the radius should be 0, not 12px") rather than re-pasting everything.
Setting the look for a whole app
All three let you describe the project before the first generation. That first message is the moment to paste a style prompt. Put it after your description of what the app does and before any feature list. Lovable also has a knowledge or custom-instructions field in project settings; the style prompt belongs there too, because chat history gets summarised and settings do not.
Snippets in a component-based tool
v0 in particular wants a component, not a class. Copy the prompt, then say "make this a Button variant named glow that accepts the same props as the default button". It will keep the values from the prompt and give you something reusable. For Lovable, ask for the CSS in index.css and the class applied in the component; that keeps it editable later.
New in CSS
These tools are conservative with new CSS because their previews run in a sandboxed iframe that may lag a browser version behind. The New in CSS prompts include the fallback line for that reason. If a feature does not show in the preview but works when you open the deployed URL, that is the sandbox, not your code.
Markdown links
None of the three fetch URLs reliably from chat, so use the clipboard. If you want the tool to see many snippets at once, paste the relevant section of llms.txt as context; it is plain text and short.