Right. And the quickest road to a theme package is the theme-cookiecutter, though having a good gander at the official docs is always a good idea!
With Lab 3 federated modules, there are a few pointy bits around fonts, but it pretty much works, and you’ve got the webpackConfig escape hatch if you really get into.
Here’s a new theme i made this week for reference… it was hand-made, not using the cookiecutter, but was informed by some of the stuff the cookiecutter does for lab3. It also shows a relatively light-weight way to make it use the theme by default. One relatively neat thing it does (currently in PR) is stack up a light and dark theme in the same CSS, reusing a common set of upstream design variables. Not recommended for the faint of heart!