Mura CMS : Override Mura's CSS settings in the Admin area.

onAdminHTMLFootRender.cfm

<cfscript>
  // this example shows how to override Mura's CSS settings in the Admin area ... 
  // you could also use jQuery or whatever other method as well.
  // Add this method to a Mura CMS SITE, THEME or PLUGIN eventHandler.cfc
	public any function onAdminHTMLFootRender($, event) {
		var str = '';
		savecontent variable='str' {
			WriteOutput('
				<style type="text/css">.mura select##restrictGroups { width:100% !important;}</style>
			');
		};
		return str;
	}
</cfscript>

Is there a way to do this for all sites, not just one?