Here is the CSS I was talking about: 

    /* Unanswered questions box */
    .status.unanswered, .status.unanswered .mini-counts, .status.unanswered strong {
         border: none;
         background-color: #833700;
         color: #FFF
    }
    
    /* Answered questions box */
    .status.answered,.status.answered .mini-counts,.status.answered strong {
        border: none;
        background-color: #65be00;
        color:#FFF;
    }
    
    /* Answer-accepted questions box */
    .status.answered-accepted,.status.answered-accepted .mini-counts,.status.answered-accepted, .status.answered strong {
        border: none;
        color:#FFF;
        background-color: #177d00;
    }
    
    /* Votecount box*/
    .votes {
        background-color: #eee;
    }
    
    /* Sidebar questions */
    .show-votes .sidebar-linked .spacer>a:first-child .answer-votes, .show-votes .sidebar-related .spacer>a:first-child .answer-votes {
        background-color: #eff0f1;
        color: #3b4045;
    }
    
    /* Sidebar answer-accepted questions */
    .show-votes .sidebar-linked .spacer>a:first-child .answer-votes.answered-accepted,.show-votes .sidebar-related .spacer>a:first-child .answer-votes.answered-accepted {
        background-color: #177d00;
        color: #FFF;
    }
    
    /* Background for accepted answers */
    div.accepted-answer {
        background-color: #e0ffe0;
    }
    
    /* Blockquote colors (needed for contrast with the accepted answer background) */
    blockquote {
        background-color:#dadada;
        border-left:2px solid #ffeb8e
    }

You can use any browser extension you like to automatically load it on mathoverflow.net. I use [Custom Style Script](https://addons.mozilla.org/en-US/firefox/addon/custom-style-script/), but any of the many similar options should work.

I am happy to do small tweaks if requested, but I want to limit the actual number of changes to a minimum. In particular I will not change the fonts, because checking that those work for all screens is complicated.

Screenshots:
[![Main page][1]][1]

[![Answer with sidebar][2]][2]

[![Accepted answer with sidebar][3]][3]


  [1]: https://i.sstatic.net/ZA4Ja.png
  [2]: https://i.sstatic.net/IjEEY.png
  [3]: https://i.sstatic.net/9PY11.png