This should be an easy-to-fix problem. Please check the following:
Make sure that the CSS files are registered properly with valid <link /> tags in the <head> of the web page. Make sure that the URLs are valid. You can try opening a CSS file URL directly from the address bar to see what happens.
Make sure that the CSS files contain valid CSS code. You can validate the CSS code at
CSS is a case-sensitive language. Make sure that the skin names set for the controls exactly match the skin suffixes in the CSS classes.
If the above still does not help, please send us a live URL to look at.
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