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As of R3 2023 release, the font icons are detached from the themes css files. If you are still using font icons, make sure to include a reference to the font icons in your applications. You can read more information about the change in the following blog post: https://www.telerik.com/blogs/future-icons-telerik-kendo-ui-themes. It contains essential information about the change for all products and migration articles to svg icons.