tailwindcss/src/plugins/margin.js

import _ from 'lodash'

export default function({ values, variants }) {
  return function({ addUtilities, e }) {
    const generators = [
      (size, modifier) => ({
        [`.${e(`m-${modifier}`)}`]: { margin: `${size}` },
      }),
      (size, modifier) => ({
        [`.${e(`my-${modifier}`)}`]: { 'margin-top': `${size}`, 'margin-bottom': `${size}` },
        [`.${e(`mx-${modifier}`)}`]: { 'margin-left': `${size}`, 'margin-right': `${size}` },
      }),
      (size, modifier) => ({
        [`.${e(`mt-${modifier}`)}`]: { 'margin-top': `${size}` },
        [`.${e(`mr-${modifier}`)}`]: { 'margin-right': `${size}` },
        [`.${e(`mb-${modifier}`)}`]: { 'margin-bottom': `${size}` },
        [`.${e(`ml-${modifier}`)}`]: { 'margin-left': `${size}` },
      }),
    ]

    const utilities = _.flatMap(generators, generator => {
      return _.flatMap(values, generator)
    })

    addUtilities(utilities, variants)
  }
}