In the section ‘Fonts’ you can change font family and font size. 

Silvera theme uses by default font ‘Roboto’ for headers and font ‘Catamaran’ for body. But you can use any Google fonts if you want.

To use any Google fonts – get Google API key for your project and enter it here (data will be updated once a week). Fonts are loaded completely – all available font sizes for the species and languages. You can do next if you want to get Google API key.

Write you Google API key and open  section ‘Fonts’ again. Now you will see a drop down menu where you can choose any Google font. You can also change the font size.