Yeah. You'd probably want CSS that looks something like

* {
  font-family: <font you want to use> !important;
}

The issue is that it would affect every single font, and many wikis design elements with specific fonts in mind.

Some alternatives are scoping the font to only apply to headings

h1, h2, h3, h4, h5, h6 {
  font-family: <font you want to use> !important;
}

Scoping it to only regular, paragraph text

p {
  font-family: <font you want to use> !important;
}

And making it only work on elements that aren't a part of .mw-parser-output, aka the wikitext output, but I couldn't figure out the CSS.