I wanted to use a font from google fonts in the common.css for a wiki. When adding it to the common.css, the font wasn't applied. Looking in the dev-tools of my browser, it listed an error stating that fonts.googleapis.com was blocked by the content security policy, preventing the font from being loaded.

The font-url in question: https://fonts.googleapis.com/css2?family=Exo+2&display=swap

The issue reported by google-chrome:

Refused to load the font 'https://fonts.googleapis.com/css2?family=Exo+2&display=swap' because it violates the following Content Security Policy directive: "font-src 'self' data: *.miraheze.org *.betaheze.org fonts.gstatic.com cdn.jsdelivr.net fastly.jsdelivr.net db.onlinewebfonts.com phab.miraheze.wiki upload.wikimedia.org".