The previously defined padding for the tab content was
overwritten to 0 by a more specific css selector. In addition,
code snippets should not have any extra padding, hence the :not(.pre)
css selector.
Pick-to: 6.3
Change-Id: I8f331924c5d01c8971660bb7a5b3aad25e3dee8a
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>