gitlabhq/app/assets/stylesheets/themes/ui_modern.scss

/**
 * This file represent some UI that can be changed
 * during web app restyle or theme select.
 *
 * Next items should be placed there
 * - link colors
 * - header restyles
 *
 */
.ui_modern {
  /*
   *  Application Header
   *
   */
  header {
    @extend .header-dark;
    &.navbar-gitlab {
      .navbar-inner {
        background: #567;
        .app_logo {
          &:hover {
            background-color: #516171;
          }
        }
        .separator {
          background: #456;
          border-left: 1px solid #678;
        }
      }
    }
  }
}