can't use $vars in supporting CSS, so put in an override.

plugins/unl_theme/css/actionNotice.php

@@ -89,7 +89,6 @@ Action Notice Box and Login Colorbox displayed to help users either register or
 		float:left;
 		height:94px;
 		width:58px;
-		background:url('<?php echo $vars['url']; ?>/mod/unl_theme/views/default/images/loginTabSlider.png') no-repeat;
 		background-position: 0 0;
     }
     #actionBar #elggOption .optionMessage{

plugins/unl_theme/views/default/css.php

@@ -18,6 +18,7 @@
 //Any elements which appear differently (or only for) non-logged in users should be imported here.
 if (!isloggedin()) {
 	echo "@import url('".$vars['url']."mod/unl_theme/css/actionNotice.php');";
+	echo "#actionBar #elggOption > a.switchAction {background:url('".$vars['url']."mod/unl_theme/views/default/images/loginTabSlider.png') no-repeat;";
 }
 ?>