This problem can be easily demonstrated by looking at the page on the demonstration page, and then copying and pasting the same code into the kendo dojo.
The official demonstration page displays the buttons like so:

But the same code on the dojo displays the buttons like so:

As you can see, the demonstration page has a consistent style for all of the buttons, while the dojo page does not.
Both pages have the same classes on the icons:
The mixture of styles gives an unprofessional impression to the customer, and is preventing me from upgrading my codebase from version 2025.4.1321
For the simplest possible example, see this dojo snippet: https://dojo.telerik.com/aroNDBBv