Add more Themes
SubEthaEdit ships with 4 Style sheets. It would be great to incorporate more of the popular color choices to provide out of the box.
This is an ongoing umbrella issue, please provide issues referencing this for each style you'd like to contribute to the main distribution.
It might be helpful to provide a template CSS for us to use as a basis from which to develop our own styles. I presume this is the purpose of the 'Show User Styles Folder'...

But as that folder is empty, it doesn't give us anything to work from, or tell us what CSS selectors are available, etc.

Yeah - that is true. In a debug build after enabling the debug menu there is style editor (see issue #11 ) that people might use as a base for these creations. Using SubEthaEdit Dark.sss or SubEthaEdit Bright.sss as a starting point would be better.
https://github.com/subethaedit/SubEthaEdit/tree/develop/SubEthaEdit-Mac/Modes/Styles
And for reference, here a screenshot from the Dark one showing all scopes in color.

Thanks. That'll give me something to work from
Also there is more documentation in the SubEthaEdit-Modes repo: https://github.com/subethaedit/SubEthaEdit-Modes/tree/master/Documentation/Styles