toc.css

<style>
  /* Table of contents */
  .table-of-contents {
    display: flex;
    flex-direction: column;
    width: fit-content;
    background: #f5f5f5;
    border: 1px solid #ddd;
    border-radius: 4px;
    font-size: 14px;
    padding: 11px;
    margin: 8px 0 30px 0;
    transition: all 0.2s ease-in-out;
  }

  .table-of-contents:hover {
    background: #ddd;
  }

  .table-of-contents h4 {
    margin: 0;
    cursor: pointer;
    transition: color 0.2s ease-in-out;
  }

  .table-of-contents h4:hover {
    color: #1d3557;
  }

  .table-of-contents ul {
    margin: 0;
    padding: 0;
    list-style: none;
    overflow: hidden;
    height: 0; /* set initial height to 0 */
    transition: height 0.2s ease-in-out;
  }

  .table-of-contents ul.show {
    height: auto; /* set height to auto when the show class is added */
  }

  .table-of-contents li {
    transition: opacity 0.2s ease-in-out;
  }

  .table-of-contents li:hover {
    opacity: 0.7;
  }
  
  
</style>