In general, such behavior is not expected but could be observed in case there is a match of class names in the application you are incorporating the Kendo widgets and the Kendo classes. You can find more details on Kendo classes in the link below, that might help pinpoint the issue:
As far as preventing the overriding I am afraid I cannot provide a valuable suggestion without additional details on what styles are being overridden. A possible approach would be to use more specific selectors in order to prevent the behavior.
You can also review this article for details on CSS precedence:
If it is possible to provide a working sample, where I can observe the behavior I might be able to provide a more detailed suggestion.
I hope this helps.
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