Is it safe to enqueue a font style without putting http or https?

Yes this is fine and is a good practice, especially if your site may switch between HTTPS/HTTP (like for a shopping cart etc) that way you are not loading mixed content.

As long as the CDN you are pulling from offers both HTTPS and HTTP you’re fine, which they do.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)