The default HTML5 validation is coming from the browsers and they internally create the elements. As these elements are internally created by the browser, the KendoReact team has no access to them to style them.
The team is currently working a Form style guidelines, which will include invalid styles. The article with the new styles and features is planned for this quarter (mid-May).
I hope that once this article and the improvements around it are out, this will help to create consistent validation messages across all browsers.
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