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

Ok, I changed "template/custom"" to be directly after "template/fonts" in template.scss. Now the font changed, but all other changes in my custom.scss are gone because they`re overwritten afterwards... So I guess I have to split my _custom.scss? Or is there a better solution?