ant-gutter.js

import declarer from '../utils/declarer'

const antGutter = decl => {
  declarer({
    body: {
      background: 'tomato'
    },
    '.one:after': {
      content: `'1'`
    },
    '.two:after': {
      content: `'2'`
    },
    '.three:after': {
      content: `'3'`
    }
  }, decl)

  decl.remove()
}

export default antGutter

declarer.js

import { pascalToDash } from './string-conversion'

const declarer = (declarations, decl) => {
  Object.keys(declarations).reverse().forEach(selector => {
    // If the selector is the same as the one the declaration was discovered in...
    if (decl.parent.selector === selector) {
      for (let declaration of Object.keys(declarations[selector])) {
        decl.parent.append({
          prop: pascalToDash(declaration),
          value: declarations[selector][declaration]
        })
      }
    } else {
      // Thanks to https://github.com/jeffjewiss for this code.
      const ruleset = decl.parent.cloneAfter({ selector })
      
      ruleset.walkDecls(decl => decl.remove())
      
      for (let declaration of Object.keys(declarations[selector])) {
        decl.clone({
          prop: pascalToDash(declaration),
          value: declarations[selector][declaration]
        }).moveTo(ruleset)
      }
    }
  })
}

export default declarer