postcss typeerror 3a require is not a function

1/* 
2    This type of setup worked for me, require calls modified
3	to suit my setup.
4	You will have to enter the postcss-* pkgs listed in your
5	package.json
6*/
7
8module.exports = (ctx) => {
9  return {
10    map: ctx.env === 'development' ? 'inline' : false,
11    plugins: [
12        require('postcss-csso')()
13    ]
14  } 
15}