Insert Icons

Built-in Images

You can use imageMso attribute to assign a built-in icon to your controls.

<button id="Button1" 
        imageMso="HappyFace" 

Custom Images

You can use the image attribute to assign a custom image to your controls
You can use the Custom UI Editor to embed custom images into a workbook file.

<button id="Button1" 
        image="custom-icon" 

More details can be found here Images > Editor - Custom Images