alt.js

const rules = []
let insert = rule => rules.push(rule)

const cxs = (css, opts = {}) => {
  const {
    child = '',
    media
  } = opts
  const className = opts.className || '_' + rules.length
  const rule = '.' + className + child + '{' + css  + '}'
  if (!media) {
    insert(rule)
  } else {
    const mediaRule = media + '{' + rule + '}'
    insert(mediaRule)
  }

  return {
    toString: () => className,
    push: (style, opts) => cxs(style, Object.assign(opts, { className }))
  }
}

if (typeof document !== 'undefined') {
  const sheet = document.head.appendChild(
    document.createElement('style')
  ).sheet
  insert = rule => {
    rules.push(rule)
    sheet.insertRule(rule, sheet.cssRules.length)
  }
}

module.exports.css = () => rules.join('')

module.exports = cxs