Under the theme Section, you can edit, remove or create a theme
In Future their can/will be companion CSS Master Files, that could compose say a “notion starter theme”, “non-profits”, “medical”, “comic book”, etc etc.
These Layer on top of all components as major modifiers.
Here are some examples, quick and dirty
Want to print your doc? This is not the way.
Try clicking the ⋯ next to your doc name or using a keyboard shortcut (