Don't theme based off ID attributes

Created by: CodeGit

Would it be possible to create a parallel set of class selectors for styles currently being applied to id?

We're currently using webpack to compile css on the new interpro design and running into problems where identity-based selectors e.g. '#global-masthead' are defined in multiple locations such as ebi-global and also theme-embl-petrol. Having class selectors would allow us to reference both styles in a single element.