'use strict'; var fs = require('fs'); var postcss = require('postcss'); var pxToViewport = require('..'); var css = fs.readFileSync('main.css', 'utf8'); var processedCss = postcss(pxToViewport()).process(css).css; fs.writeFile('main-viewport.css', processedCss, function (err) { if (err) { throw err; } console.log('File with viewport units written.'); });