CSS: Change tooltip container to be only relative when tooltip is shown

[lscharmer]

This PR fixes Mantis Bug: https://mantis.ilias.de/view.php?id=46262 As the Permanent link makes use of the Help Topics (so the same issue occurs if a button with Help Topics is displayed below a dropdown).

This PR changes that the help topics container (where the corresponding element lies) will only be made relative when it is active, as relative breaks the normal z-index rules and will always be displayed on top of other objects.

As the relative property is only used to position the active tooltip, this doesn't break anything else of the help topic.