The headings are using
ui-sans-serif. The body text is
ui-serif. The code and the pre elements are using
In typography, a serif is a small line or stroke regularly attached to the end of a larger stroke in a letter or symbol within a particular font or family of fonts.
- Serif - Wikipedia
In typography and lettering, a sans-serif, sans serif, gothic, or simply sans letterform is one that does not have extending features called "serifs" at the end of strokes. Sans-serif typefaces tend to have less stroke width variation than serif typefaces. They are often used to convey simplicity and modernity or minimalism.
- Sans-serif - Wikipedia
monospaced font, also called a fixed-pitch, fixed-width, or non-proportional font, is a font whose letters and characters each occupy the same amount of horizontal space. This contrasts with variable-width fonts, where the letters and spacings have different widths.
console.log("Hello world"); document.body.textContent = "Hello World!";
- Monospaced font - Wikipedia