type

Most interfaces are 90% text. If the text is defaulted, the interface is defaulted, and no amount of colour or motion hides it.

Choosing the family

One sans for the interface. One mono for data, code, shortcuts and labels that should read as system. A display face only on marketing pages, and only if the sans cannot carry it.

Pick for the job:

Job	Traits	Reach for
Dense product UI	Neutral, tight apertures, good at 12–14px, tabular figures	Geist, Inter, SF-adjacent grotesks
Reading (docs, articles)	Larger x-height, wider spacing, optical sizing if available	Source-style humanists, or the same sans at 16px+ with looser leading
Data, code, labels	Mono with clear 0/O and 1/l, ligatures optional	Geist Mono, JetBrains Mono, Berkeley Mono
Display	Has an opinion; pairs by contrast with the sans, not similarity	one, chosen against the brand

If the project already has a family, use it. Changing fonts is a redesign, not a fix.