CSS Improvements for Feedback Page

[joelit]

Description of the enhancement

• [ ] The footer should be white and it should line up with the main content
• [x] The background colour should be according to the spec
• [x] The margin between header and main content should be wider
• [x] The Skosmos logo should not repeat
• [ ] The background image is not set
• [ ] Vocabulary selection arrow should be clickable