ISIS-537 Minor improvements to the CSS of AboutPage
ISIS-537 Use fixed top navigation bar.

https://trello.com/c/KuelbIOY/63-header-should-be-fixed
ISIS-537 Improve the styling of the bookmarks panel

https://trello.com/c/lTjy3n6u/64-styling-of-bookmarks-is-different-doesn-t-follow-theme