Image inside <summary>

content:url('/path/to/file.png')

by Jason Cravens

HTML

<details>  
  <summary>Click to expand dropdown</summary>    
  <div class="image-container">    
    <a href="https://google.com">    
      <span style="content:url('https://r7.hiclipart.com/path/133/147/693/arrow-bullet-computer-icons-bullet-holes-e2beb2b74def46ebed678b15bb0e8012.png');width:100px;height:100px"></span>
    </a>
  </div>    
</details>