discourse/app/assets/stylesheets/mobile/sidebar.scss

#main-outlet-wrapper {
  .sidebar-section-header {
    margin-bottom: 0.25em;
  }
  .sidebar-section-header-link {
    font-size: var(--font-0);
  }
  .sidebar-section-link {
    padding: 0.5em;
    font-size: var(--font-0);
  }
}