Change font on inherited theme

I want to change the font on a child theme (of Antimatter). I added the @font-face to my _custom.scss and assigned it to "$font-family-default". But nothing changes on the site.
Is it not possible to override scss-variables in _custom.scss? I also changed "custom" to the last line in template.scss

oh, sorry for the double-post. Something went wrong with login and account-generation :(