TIF_E41201544/public/assets/scss/demo2/_layouts.scss

// Backdrop for header in mobile/tablet
.header-open {
  .horizontal-menu {
    &::before {
      content: '';
      width: 100vw;
      background: rgba($modal-backdrop-bg, $modal-backdrop-opacity);
      position: fixed;
      top: 0;
      bottom: 0;
      right: 0;
    }    
  }
}