install

pip3 install ungog

usage

ungogmycss main.css
[+] got https://fonts.googleapis.com/css?family=Gruppo|Scope+One
[+] got https://fonts.gstatic.com/s/gruppo/v7/uU5IFiQZ8WKPhrRfLBLURw.ttf
[+] replacing from:   src: local('Gruppo'), url(https://fonts.gstatic.com/s/gruppo/v7/uU5IFiQZ8WKPhrRfLBLURw.ttf) format('truetype');
[+] replacing to:     src: local('Gruppo'), url('fonts/gruppo.ttf') format('truetype');
[+] got https://fonts.gstatic.com/s/scopeone/v2/_52Fm41u4u2R3EEH0A9bn6CWcynf_cDxXwCLxiixG1c.ttf
[+] replacing from:   src: local('Scope One'), local('ScopeOne-Regular'),
    url(https://fonts.gstatic.com/s/scopeone/v2/_52Fm41u4u2R3EEH0A9bn6CWcynf_cDxXwCLxiixG1c.ttf)
    format('truetype');
[+] replacing to:     src: local('Scope One'), local('ScopeOne-Regular'),
    url('fonts/scope_one.ttf') format('truetype');
[+] done

and then you should be ready to replace your original file with main.css.new. do not forget to include the new fonts/ folder into your local assets.