AUTHOR: Marin Bratanov
DATE POSTED: December 11, 2018
CSS validation over the Telerik UI for ASP.NET AJAX stylesheets fails and finds invalid values or non-existing rules.
Sometimes tools like ReSharper or the w3.org CSS validator are used to validate the CSS on a site and that includes the stylesheets for the Telerk controls.
Invalid values or non-existing rules are often reported, because our stylesheets contain a number of browser hacks or vendor-specific rules that are necessary to work around browser issues so the controls can look as expected.
You can find the majority of the flagged rules in sites like http://http//browserhacks.com/
Thus, while the values are technically invalid, the browsers that need to understand them will work with them as expected, and you can ignore such warnings for CSS validation issues stemming from the Telerik UI for ASP.NET AJAX suite.