Updated css formatting

[ggemre]

No description provided.

[ggemre]

@seirin-blu
This PR contains some CSS format fixes, I made these changes locally in my firefox configuration and decided to push them here for your convenience. Feel completely free to use&merge / disregard&close this PR. I included an overview of the changes I made below for reference since formatting updates can be hard to read through:

Changes to style:

• unified spacing
  • each block separated with 1 blank line
  • blank lines within blocks removed
  • element selectors consistently use 1 space when necessary
• made indentation more consistent
• lines longer than 100 chars wrapped appropriately (excluding comments)
• indented sub blocks
• made 1-liner css blocks span multiple lines

2 Non-style changes to be aware of:

• line 229 of userChrome.css:

   #tabbrowser-tabs {
   -  background-color: #none !important;
   +  background-color: none !important;
   }

• line 90 of about-preferences.css

   #categories > .category.selected:hover:active {
   -  color: #1a1a1a !important !important;
   +  color: #1a1a1a !important;
      background-color: #b24747 !important;
   }

Much of the styling changes were based on my own opinion, by all means let me know of anything to change or feel free to use this PR how you'd like.

[seirin-blu]

Hello,

Thanks for doing this pull request.

Halo isn't really super actively maintained despite me using it as my primary config on Firefox, so updates are slow. I'll be sure to take a look at your pull request at some point and merge if it doesn't change anything too drastic. May add/change some other stuff in Halo as well at the same time