Steps to Reproduce

 run fiddle in iceblue:

https://zkfiddle.org/sample/19s0qi9/1-toolbar-overflow-popup

Current Result

To change the toolbar icon, this sample use a custom sclass and redefine the icon content

Expected Result

 <toolbar overflowIconSclass="z-icon-home" >

Debug Information

• At the time we implement this feature, if zk drops IE 11, we can implement this with CSS custom properties
   

  Workaround

use css to replace the icon manually

  <style>
    .custom-icon .z-toolbar-overflowpopup-button:before{
        content: '\f0c9'; //charcode for the menu icon (from font-awesome icon list)
    }
  </style>