What do I type into <custom-font>|<font-url> to add font to Javascript iframe in Avenue 7.0?

Hello,

I've managed to successfully add a custom font (Bodoni Egyptian) to my Squarespace 7.0 site (Avenue template):

<link rel="stylesheet" href="https://use.typekit.net/kzw2kxp.css">

I've also managed to embed a Javascript iframe for puzzles into my site, from an outside developer. Now I just want to match the font in the iframe with my Squarespace font (replacing the Georgia font). For this I need to type something into a field that reads:

<custom-font>|<font-url>

Can someone tell me where to find the URL and what exactly to type? I suspect part of the answer is in my Website Tools/Custom CSS:

<link rel="stylesheet" href="https://use.typekit.net/kzw2kxp.css">

But I don't know exactly how to do it.

Thank you!