text: const postcss = require('postcss');
  const retina = require('../lib');
  const fs = require('fs');
  const path = require('path');
  
  
  const processor = postcss([retina]);
  
  fs.readFile(path.resolve(__dirname, './border.css'), 'utf8', (err, input) => {
      if (err) return;
  
      processor.process(input, {
          from: './border.css',
          to: './border.retina.css'
      }).then((result) => {
          fs.writeFile(path.resolve(__dirname, './border.retina.css'), result.css);
      });
  });
  