1. Instead of only supporing the creation of unstyled labels like

ui::label("...").foreground(...).background(...)

higher level functions like

ui::label::primary("...")
ui::label::ternary("...").dim()

should be provided.

2. Use labels instead of Cell and Span where possible.

3. Clarify fg / bg / dim vs. style interface on labels (dim in reversed styles not considered)