Best way of working with a designer?

I know CSS enough to be dangerous but I'm slow at it. Also, anything I design ends up looking like a corporate intranet app from the late 1990s.

So I hired a talented designer. I'm very happy with their work, but I'm finding that integrating their design is slow and error prone. Why? They create beautiful HTML and CSS files, which are very hard for me to pick apart and apply to my individual components. And once I do that, the HTML+CSS is spread out over many files, so the designer can't tweak the design for the next version. The designer doesn't know Vue.js (I suspect most don't) so I can't expect them to update the component files themselves.

Does anyone have any good tips for how to collaborate with a designer when you're a Vue.js developer? I have to think this problem has been solved by someone.

Looking forward to hearing your thoughts!