Epic improvements and important fixes.

Fixes:

 - Drop-down menu scroll mechanism when the height is longer than the view
 - TOC rendering issues
 - Link styling inconsistencies
 - Breadcrumbs rendering issues

Changes / improvements:

 - Design style of TOC
 - Design style of Breadcrumbs 
 - Design style of Drop-down menus (mobile and desktop)

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)