Why not use CSS (instead of `data-depth="0"`) to style the ToC?

    /* Use `ul ul` so it does not apply to top-level list items */
    .media-tabs .contents > ul ul > li > .title::before {
     display: inline-block;
     margin-right: 5px;
     font-weight: bold;
     color: @brand-primary;
     counter-increment: section;
     content: counters(section, "-") ".";
    }