I have prepared an example: http://dojo.telerik.com/oZOYa
In my project setup I use 24x24 px images with transparent background (in the online demo 16x16 px), which I position in the center of the buttons (css vertical-align). I also need to set the button click event handlers after the toolbar has been initialized.
On desktop browsers the example works well. However, when I use Chrome for Android (version 58), the button click event is not always firing, even when the orange button background flashes up, when pressing on a button. The issue seems to appear more often, when the page is zoomed. Toggle buttons work fine. I experience the same issue, but less often, with iOS 9.3.2 Safari too.
Any ideas on how to improve the user experience?