code: function(cssSelector) {
  
          function getAfterContentValue(qs) {
  
              var el = document.querySelector(qs);
              var styles = el ? window.getComputedStyle(el, ':after') : null;
  
              return styles ? styles.getPropertyValue('content') : '';
          }
  
          return driver.executeScript(getAfterContentValue, cssSelector);
      }
docs: Get the content value of a :after pseudo element
  @param {string} cssSelector - css selector of element to inspect
  @returns {Promise} executes .then with value
  @example
  helpers.getPseudoElementAfterValue('body header').then(function(value) {
  console.log(value);
  });