Ability to use `className` instead of CSS variables

[o-alexandrov]

Summary

When a project uses PigmentCSS to style emails and web to reuse a single theme (for colors and typography), it currently faces two problems:

1. Inability to run in a non-browser environment [core] Errors thrown in non-browser environment (unsafe when referenced) #8 Support runtime / "non bundler integration" mode? #59 when running ReactDOM.prerender (needs extra bundling)
2. Emails don’t support CSS variables

This issue asks to introduce an option to generate class names, instead of CSS variables.

Search keywords: css variables vars emails