// Open Fiddler and Choose "Rules" menu, click "Customize Rules..." and add this code to CustomRule.js

class Handlers
{
    // ....
    public static RulesOption("Hide CSS")
    BindPref("fiddlerscript.rules.HideCSS")
    var m_HideCSS: boolean = false;
    // ....
    static function OnBeforeResponse(oSession: Session) {
        // ....
        if (m_HideCSS && oSession.oResponse.headers.ExistsAndContains("Content-Type", "text/css") )
		    {
            oSession["ui-hide"] = "true";
        }
	    	// ....
    }
}