We've done it so many times...
The designs for the new site had a very nice contact form on them and we've carefully crafted a beautiful HTML form and styled it accordingly; only to realize that the markup we get from UmbracoForms doesn't even remotely resemble our home-brewed flavor, and we'll need to do some serious reworking of our CSS to get the desired output.
This is my collection of Kit partials for creating an UmbracoForms mockup when styling frontend components.
Currently Work-In-Progress ...