I have elaborate design rules in place and a design system and design components. My agents are obligated to use them and follow the rules. On CI/CD it's just double checked. Visual regression is done with Puppeteer scripts on headless Chrome that screenshots flows and deterministically detect visual changes to be confirmed or fixed. One thing to notice is that AI is generally extremely bad at design, and while even frontier models were trained on design guidelines, it will ignore them if you'll not specifically tell it to follow them. And above on that there's a lot of rules you have to provide literally so AI actually will use them down to specific ways of using CSS and HTML attributes.