https://jameshfisher.com/2024/03/12/a-formula-for-responsive-font-size/
This CSS is now part of most websites I make:
:root {
font-size: calc(1rem + 0.25vw);
}
This rule is an alternative to @media rules like this from nytimes.com:
p { font-size: 1.125rem; }
@media (min-width: 740px) {
p { font-size: 1.25rem; }
}
This pattern is the norm: a small font size, a large font size, and a breakpoint. Here’s a sample of common sites:
Small font-size Large font-size Breakpoint
Medium.com 1.125rem 1.25rem 728px
Substack.com 1.125rem 1.25rem 768px
Nytimes.com 1.125rem 1.25rem 740px
But breakpoints are mathematically ugly! Instead of defining font-size piecewise, can’t we use one linear function? Here’s the line I believe they’re trying to approximate:
With modern CSS, we can just write that function! It’s calc(1.0625rem + 0.2604vw). I round this to 1rem + 0.25vw.
Sharp-eyed readers might wonder: doesn’t my CSS have circular reasoning? If rem is defined as “Font size of the root element”, how can we use 1rem in the definition of font-size on the root element?! It turns out it’s a special case:
When specified in the font-size property of the root element, or in a document with no root element, 1rem is equal to the initial value of the font-size property.
