Fixed left vertical navigation layout

I have tried to follow this tutorial, but no nav appears https://generatepress.com/forums/topic/fixed-left-vertical-navigation-layout-css-and-customizer-only/
I'm using this code

@media (min-width: 769px) {
  .site-header {
    display: none;
  }

  #primary-menu.main-nav {
    width: 20%;
    height: 100%;
    position: fixed;
    top: 0px;
    left: 0px;
    opacity: 1;
    padding-top: 175px;
    background-color: #1a2930;
    background-image: url("http://bluepointdigital.com/sites/create/elle/wp-content/uploads/sites/3/2016/09/1442274824.png");
    background-repeat: no-repeat;
    background-position: top center;
    border-style: hidden;
    border-top-width: 65px;
    border-top-style: solid;
    border-top-color: #1a2930;

  }

  .footer-widgets {
    padding-left: 20%;
  }

  .site-info {
    padding-left: 20%;
  }
}

but nothing appears on desktop