Grunt CSS Minify Example

gruntfile.js

module.exports = function(grunt){
    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),
        
        cssmin: {
            my_target: {
                files: [{
                    expand: true,
                    cwd: 'css/',
                    src: ['*.css', '!*.min.css'],
                    dest: 'css/',
                    ext:'.min.css'
                }]
            }
        }
    });
    
    grunt.loadNpmTasks('grunt-contrib-cssmin');
}; 

package.json

{
  "name": "grunt",
  "version": "1.0.0",
  "devDependencies": {
    "grunt-contrib-cssmin": "^0.13.0"
  }
}