A 'raw' theme, without any styles applied

Prerequisites

• I have read the documentation

What theme are you using?

core

Is your feature request related to a problem? Please describe.

I would like to control the UI of the form, but currently using the "core" library assumes usage of Bootstrap.

Describe the solution you'd like

1. A "raw" version of the form, with no classes/styles applied.
2. A way to apply/override classes to specific elements, at a global level, for example:

{
    field: "my-field-class",
    input: "my-input-class",
}

Describe alternatives you've considered

What I am currently doing is copying all the code for the core library, and adding a class to style with CSS.

I don't like this approach as this also duplicates logic (and I'm not changing any of that, literally adding a class, so I can then override bootstrap) - I feel this leaves me vulnerable to breaking changes.