Handbook names trigger link hover styles

[Clorith]

The current CSS for the handbook pages triggers underlines on the handbook name inside .handbook-name, which pushes the title to the left and adds the scroll buttons to the right (the underline is pushed below the fold).

[Clorith]

Attached patch adds hiding of overflow elements on the y axis as well as the x axis which should take care of the scrolls

[coffee2code]

In 1214:

WP.org P2 child theme: Prevent handbook name from triggering vertical scrollbar on hover.

Fixes #740.
Props Clorith.