System Fonts

System Fonts enqueues a stylesheet that lets you use the native font on each operating system and defines a system-ui css @font-face that you can use on the customizer, your theme’s settings or your own code.

Usage example

The Twenty Seventeen theme uses this css selector for the body text:

body, button, input, select, textarea { font-family: "Libre Franklin", "Helvetica Neue", helvetica, arial, sans-serif; } 

We are going to replace it with the default system font.
In you WordPress site, go to Appearance > Customize > Additional CSS and paste this code

body, button, input, select, textarea { font-family: system-ui; } 

Appart from them font-family, there are other font-properties available:

• font-style: normal or italic;
• font-weight: 300 (light), 400 (regular), 500 (medium), 700 (bold);

For example this is the code make an element’s text semibold and cursive:

#my-element { font-family: system-ui; font-weight: 500; font-style: italic; }