I loved it when we could declare different font sizes between breakpoints to have the best typography for the given width, but when the typography locks were introduced things go a whole lot better.
Fluid typography is the idea that
font-size(and perhaps other attributes of type, like
line-height) change depending on the screen size (or perhaps container queries if we had them).
The core trickery comes from viewport units. You can literally set type in viewport units (e.g.
font-size: 4vw), but the fluctuations in size are so extreme that it’s usually undesirable. That’s tempered by doing something like
font-size: calc(16px + 1vw). But while we’re getting fancy with calculations anyway, the most common implementation ended up being an equation to calculate plain English:An excerpt from Simplified Fluid Typography
I want the type to go between being 16px on a 320px screen to 22px on a 1000px screen.