Customize font using CSS for fonts already in the squarespace library

I would like to change my paragraph 3 font to a font already in the squarespace font library  (e.g. Shelby). Every article/tutorial I've seen for custom CSS requires an src url for the font. The tutorials I've seen show you how to grab the url for custom fonts that the end user uploads into squarespace. However, I don't know how to find the src url for fonts that are already in the squarespace font library. Can someone help with that?

PS my website isn't live yet, so I can't share the link to it here.

You just need to know the font family name, what is the font family?

// Paragraph 3 font family
.sqsrte-small {
   font-family: 'font name here';
}