Gruntfile.js

module.exports = function (grunt)
{
    'use strict';

    // Load all Grunt tasks.
    require('load-grunt-tasks')(grunt);

    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),

        // Set up paths.
        paths: {
            src: {
                sass: 'src/sass/'
            },
            dest: {
                css: 'dist/css/'
            }
        },

        // Clean distribution directories/files to start afresh.
        clean: [
            '<%= paths.dest.css %>'
        ],

        // Add vendor prefixed styles and other post-processing transformations.
        postcss: {
            options: {
                processors: [
                    require('autoprefixer'),
                    require('cssnano')
                ]
            },
            dist: {
                src: '<%= paths.dest.css %>*.css'
            }
        },

        // Sass configuration.
        sass: {
            options: {
                implementation: require('sass'),
                outputStyle: 'expanded', // outputStyle = expanded, nested, compact or compressed.
                sourceMap: false
            },
            dist: {
                files: [
                    {'<%= paths.dest.css %>style.css': '<%= paths.src.sass %>style.scss'}
                ]
            }
        },

        // Directories watched and tasks performed by invoking `grunt watch`.
        watch: {
            sass: {
                files: '<%= paths.src.sass %>**/*.scss',
                tasks: 'build'
            }
        }

    });

    // Register tasks.
    grunt.registerTask('build', ['clean', 'sass', 'postcss']);
    grunt.registerTask('default', ['watch']);
};