Fixed sticky MR tabs positioning when sidebar is pinned

Phil Hughesrequested to merge
sticky-mr-tabs-pinned-nav into master

What does this MR do?

The sticky MR tabs where positioned underneath the pinned sidebar. This fixes that by accounting for the size of the pinned nav.

Screenshots (if relevant)

Screen_Shot_2016-10-28_at_09.37.18

What are the relevant issue numbers?

Closes #23926 (closed)

Merge request reports