Reduce width to 2/3 of page
Hide nav when below 600px
Make H1 headers bold
Tweak nav design

Should match this:
https://www.gov.uk/government/policies/informing-the-debate-on-scotlands-constitutional-future
Align nav with content
Add space between title and content
Same text in high volume services as in all services
Merge pull request #129 from alphagov/fix-about-page

Fix about page