blessed-rs/styles/toc.scss

.toc {
      position: sticky;
      overflow-y: auto;
      top: 24px;
      max-height: calc(100vh - 24px);

      ul {
          list-style: none;
          padding: 0;
      }

      li {
          padding-left: 0;
          margin: 3px 0px;
          font-size: 1em;
          > a {
              color: #999;
              text-decoration: none;
            }
          > ul {
              /*display: none;*/
          }
      }
      
      > ul > li.active:not(.active ~ .active) {
          > a {
              color: #333;
              text-decoration: none;
          }

          // Sub-lists
          > ul {
              display: block;

              > li.active:not(.active ~ .active) > a {
                  color: #333;
                  text-decoration: none;
              }
          }
      }
}

.subtoc {
    margin-left: 12px;
}
.subtoc li {
    font-size: 0.85em;
}