9/UI/metabar slates not visible in Safari 40968

[catenglaender]

https://mantis.ilias.de/view.php?id=40968

Issue

(Some) Metabar slides do not appear on mobile breakpoint in Safari/Webkit.

Change

The issue seems to be caused by overflow-x: clip; on the header, which no longer seems to be needed as currently no unwanted scrollbars seem to form. Strangely, overflow-x: clip; is actually supported by Safari/Webkit, just something along the chain of position: sticky; and position: absolute; causes a broken rendering (y expansion also gets clipped).

Impact

Removing overflow-x: clip; which was likely introduced to combat an unwanted scrollbar might cause said scrollbar to show up again under conditions that I can currently not reproduce. If there now is an unwanted scrollbar appearing, it's probably wise to directly fix the cause of the scrollbar rather than to clip the header.