installing Closure Compiler on debian Nginx
Closure Compiler does not minify CSS files, just JS files. For that you want: https://github.com/google/closure-stylesheets
Closure Compiler isn't a good choice if you want to minify arbitrary JS files without testing the result. It doesn't back off when faced with eval or with or IE's conditional code like some other compression tools do.
If you are using Apache perhaps you might like Google's PageSpeed module which is designed to work in the general case.