Add topbar-container css hook

[danmichaelo]

At the moment I'm not sure if it's possible to make the frontpage topbar look the same as the topbar on other pages with just CSS, since the outer div is missing on the frontpage.

This PR adds an outer div to the frontpage topbar, which makes it easier to style the frontpage topbar as you like. I've added a class name "topbar-container", but otherwise kept the old class names, so I wouldn't expect this change to break anyone's CSS.

Frontpage

+ <div class="topbar-container topbar-frontpage">
    <div class="topbar frontpage">

Non-frontpage

- <div class="topbar-white">
+ <div class="topbar-container topbar-white">
    <div class="topbar topbar-white">

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Merging #1159 (f988ad2) into master (4a050f4) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1159   +/-   ##
=========================================
  Coverage     67.97%   67.97%           
  Complexity     1584     1584           
=========================================
  Files            32       32           
  Lines          3888     3888           
=========================================
  Hits           2643     2643           
  Misses         1245     1245           

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[osma]

Thanks! Looks good to me and doesn't break the Finto layout which is obviously a plus ;)