One can use Phil Brown's custom CSS [here](https://stackapps.com/questions/9296) to get part of the older layout back:

<img src="https://i.sstatic.net/F98X3.png" width="500">

Denis Nardin's [previous CSS](https://meta.mathoverflow.net/a/4032) partially works (quote backgrounds are still coloured gray and accepted answer backgrounds are still coloured green), but the [brown/green/dark green] style for answers broke. as the css class name for unanswered questions (.status.unanswered) got merged with the one for votes (.s-post-summary--stats-item).

Here's a Franken-CSS that combines the above two styles:

    /** Container **/
    
    .s-post-summary {
      padding-left: 8px;
    }
    
    /** Stats grid **/
    
    .s-post-summary--stats {
      display: grid;
      width: unset;
      grid-template-areas:
        "score answers views"
        ". bounty ."
        ;
      grid-template-columns: repeat(2, 1fr); /* change to 3 for views */
      column-gap: var(--s-post-summary-stats-gap);
      row-gap: var(--s-post-summary-stats-gap);
      align-content: start;
      align-items: center;
    }
    
    .s-post-summary--stats .s-post-summary--stats-item,
    .s-post-summary--stats .s-post-summary--stats-item.has-answers {
      display: flex;
      flex-direction: column;
      margin: 0;
      padding: 4px;
      width: 60px;
    }
    
    /** State grid items **/
    
    .s-post-summary--stats .s-post-summary--stats-item .s-post-summary--stats-item-number {
      font-size: larger;
      margin-right: 0 !important;
    }
    
    .s-post-summary--stats .s-post-summary--stats-item:nth-child(1) {
      grid-area: score;
      border: none;
      background-color: #eee;
      border-radius: 0px;
      color: #3b4045
    }
    
    .s-post-summary--stats .s-post-summary--stats-item:nth-child(2) {
      grid-area: answers;
      border: none;
      border-radius: 0px;
      background-color: #833700;
      color: #FFF
    }
    
    .s-post-summary--stats .s-post-summary--stats-item.has-answers {
        background-color: #65be00;
        color:#FFF;
    }
    
    
    .s-post-summary--stats .s-post-summary--stats-item:nth-child(3) {
      grid-area: views;
      border: none;
      border-radius: 0px;
    }
    
    .s-post-summary--stats-item.has-bounty {
      grid-area: bounty;
    }
    
    .s-post-summary--stats .s-post-summary--stats-item.s-post-summary--stats-item__emphasized {
      color: var(--fc-light);
    }
    
    /** Tags **/
    
    .post-tag.s-tag__watched {
      padding-left: 0.5em;
    }
    
    .post-tag.s-tag__watched:before {
      content: none;
    }
    
    /** Hide unwanted elements **/
    .s-post-summary--stats .iconCheckmarkSm,
    .s-post-summary--meta .s-avatar {
      display: none;
    }
    
    .s-post-summary--stats-item.has-accepted-answer {
        color:#FFF;
        background-color: #177d00;
    }
    
    /* Part of Denis Nardin's Original CSS (some of it merged above) */
    
    /* 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
    }
    
    /* Background on questions with watched tags in the question list */
    .question-summary.tagged-interesting {
     background-color: #fff5deb3;
    }

It gives the following result:

<img src="https://i.sstatic.net/dv7Hg.png" width="500">

To enable it, follow the steps below:
 1. Install a browser extension allowing you to load custom CSS onto pages, such as Stylus ([Firefox Link](https://addons.mozilla.org/en-US/firefox/addon/styl-us/), [Google Chrome link](https://chrome.google.com/webstore/detail/stylus/clngdbkpkpeebahjckkjfobafhncgmne?hl=en)).
 2. Go to the MathOverflow homepage and click the Stylus icon:
[![enter image description here][1]][1]
 3. Go to "Write style for: mathoverflow.net/this URL".
 4. You'll be met by this screen:
[![enter image description here][2]][2]
 5. Paste the above CSS into the "Code 1:" section.
 6. Save via the left sidebar.
 7. Everything should now be working again.

  [1]: https://i.sstatic.net/vjQeL.png
  [2]: https://i.sstatic.net/QZhFV.png