Update footer webform styles

I've merged the updated styles. But now we need a preprocessor to get the webform category and add the class to the form attributes.

For the footer the category = "footer"

The rendered class = "webform-category--footer"

We might not need a preprocess at all; let me see if I can add the requisite classes to the webform’s configuration directly.

Was able to add the webform-category--footer class to the webform without changing Mercury. It looks good!