DiscoTOC/scss/sidebar.scss

.discourse-sidebar .d-toc-regular .d-toc-article .row {
  width: 75%;
  @media screen and (max-width: 1200px) {
    width: 65%;
  }
}

.mobile-view .discourse-sidebar .d-toc-regular .d-toc-article .row {
  width: 100%;
}