You are missing the closing parenthesis after the URL. Also, the intent is that you replace "__FONT NAME__" with the actual name you want to use.

Beside what Andrewds said:

The error reported for line 10 can be ignored.

The editor is outdated and doesn't understand :is( )

I've done the suggestions you guys said but nothing changed and the font hasn't applied yet. Did I do something wrong? (edit: it worked. thanks)

The editor is outdated but technically :is() is a de facto standard since the official documentation is still in the working draft phase. As is usually the case these days, early adoption is driven by the 3 largest desktop web browsers: Chromium (>70% market share), Safari (~18.2% market share), Firefox (~2.7% market share).