Move inline style to static css file

[nicksellen]

What does this PR do?

We had some inline style on the homepage for the splash landing. I moved this to an external file.

Links to related issues

#1068

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #karrot-dev channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, pull request link, username(s))

[codecov]

Codecov Report

Merging #1143 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1143   +/-   ##
=======================================
  Coverage   60.87%   60.87%           
=======================================
  Files         224      224           
  Lines        3737     3737           
  Branches      620      633   +13     
=======================================
  Hits         2275     2275           
  Misses       1461     1461           
  Partials        1        1

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