Cleanup SCSS to prevent mass re-imports.

[jmchilton]

These are imported as part of base.scss.

The relevant change is in 0b262c0#diff-f93bafd11ed7133c2cb9ab50021a3d29e5ce689d4292d758daa2ae6353d213ae.

Are there downsides to importing all of base.scss in here? I cannot get my downstream branch in #19377 to compile at all when I use components that import _form-elements.scss now 😢. Can we get away with a lighter import than was done 0b262c0?

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.