Restoring previous design tweaks

[tagawa]

Description :

Restoring changes to duck.co design (CSS only) from November 2017.

Reviewer notes :

References issues / PRs:

For reference, here are the previously merged PRs:

• https://github.com/duckduckgo/community-platform/pull/1500
• https://github.com/duckduckgo/community-platform/pull/1502
• https://github.com/duckduckgo/community-platform/pull/1503
• https://github.com/duckduckgo/community-platform/pull/1504

Who should be informed of this change?

@jbarrett

Does this change have significant privacy, security, performance or deployment implications?

Don't think so.

Checklist :

• [ ] Back end tests (perl, scripts)
• [ ] Front end tests (js, integration)
• Browser verification
  • [ ] IE
  • [ ] Chrome
  • [ ] Firefox
  • [ ] Safari
  • [ ] Opera
• Mobile verification
  • [ ] iOS
  • [ ] Android