Theme & Design Tokens
The editor's visual system and how to restyle it.
The shared component layer.
app/editor/components/primitives/ factors the control-room look out of per-component inline styles: Panel with PanelHeader and PanelBody, Button, Chip, ListRow, Field, and the Icon set.
Compose these rather than re-deriving colours, borders and spacing. Every visual value in them traces back to a token.