How to get a asp:Panel's CSS Class in code-behind after it has changed by CSS

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I have a Panel control who's class is changed via javascript. When the user click a button, I need to check the Panel's css class and if it is the changed value, then I need to do stuff. The problem is, once I change the css class using Javascript, the server is not getting that information back. I need the server to recognize that the class has changed. I have attempted __doPostback but that messes up many of the elements on the page. Looking for suggestions. Thanks