Add in theming functionality to libraries that support it

[DSchau]

Description of Issue

Theming is a big win in CSS in JS solutions; should build it in!

Proposed Solution (if applicable)

I'd create a theme.js with the relevant shared style code. From here, I'd use a ThemeProvider to share that theme between each child component

Note: PRs are always sincerely appreciated! If fixing an issue, simply do fixes #{COMMIT_NUMBER}, i.e. fixes #20, and Github will automatically close the issue when the PR is merged.

Thank you for your contribution(s)!