code: function px (val, el) {
    const container = el || document.body
  
    if (!val || typeof val === 'number') {
      return val
    }
  
    const [ num, unit ] = parseUnit(val)
  
    if (unit === 'rem') {
      return num * getFontSize()
    } else if (unit === 'em') {
      return num * getFontSize(container)
    } else {
      return num
    }
  }
docs: ---
  category: utilities
  ---
  Converts a unit value size combination (em, rem, px) to a number representing px
  
  Example inputs:
  - '100rem'
  - '20em'
  - '40px'
  
  @module px
  
  @param {String} val
  @param {DomNode} el - containing element, for context measure is em (defaults to document.body)
  @returns {Number} Returns numerical representation of pixels