Which CSS property changes the font family?

The CSS property that changes the font family is font-family.

A font family is a typeface grouping, such as Arial, Georgia, or “Times New Roman.” The font-family property tells the browser which family to use when rendering text. Authors can provide a comma-separated fallback list, allowing the browser to try alternatives when a preferred font is unavailable: font-family: Arial, Helvetica, sans-serif.

The final generic family, such as serif, sans-serif, or monospace, is useful because browsers can select a broadly matching fallback. Names containing spaces are conventionally quoted, although CSS also accepts some unquoted names. Modern sites can load additional fonts with @font-face, then reference them through font-family.

Common mix-ups involve the related font properties. font-size changes scale, font-weight changes thickness, and font-style changes slant, such as italics. The property chooses the family; those other properties adjust characteristics of the chosen text design. The actual result can still vary with font files, browser behavior, operating-system substitution, and user settings.