How to allow @ symbol to minify in grunt uglify (css)?

Question

Grunt.js

Good evening! :)
I collect .css files with a primer, but when minimizing (uglify), an error occurs due to the @ symbol (font import). Help with a problem :)

>> Uglifying source build/styles.css failed.
Warning: Uglification failed.
Unexpected character '@'. 
Line 1 in build/styles.css
 Use --force to continue.

Thank you!

Answer 1

Better use https://www.npmjs.com/package/grunt-contrib-cssmin
Uglifyjs not for css.