code: function isUsingDefaultTheme( element ) {
  
      var theme,
          prop = 'position'
  
      // For IE.
      if ( element.currentStyle ) {
          theme = element.currentStyle[prop]
      }
  
      // For normal browsers.
      else if ( window.getComputedStyle ) {
          theme = getComputedStyle( element )[prop]
      }
  
      return theme == 'fixed'
  }
docs: Check if the default theme is being used.