Stopping Wikipedia Zero X close button from overlaying elements.

* Carrier banner text is being overlaid by the Zero X close button.
* Fix uses relative positioning, because Zero X button in <div>.
* float: right is set. ResourceLoader RTL/LTR can change on fly.
* margin: 3px set to ensure safety on all sides of element.

Change-Id: I5315f3c1ea99b21e0a1cbe924b0f783950bb2582