Thank you for contacting us. The buttons in spell dialog are placed into an unordered list (UL) and the sqares that you see are most probably generated by a global CSS styles applied to all UL elements. Most probably, it looks similar:
Another option is that the styles are loaded a little slowly and it takes some time for them to be applied.
If you could send us a sample code with the existing issue or a live url, we`ll be able to give you more detailed information about the issue.
All the best,
the Telerik team
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