@media (max-width:900px) {

  #nav ul {
    display:none;
    flex-direction:column;
    background:#000;
    position:absolute;
    top:80px;
    right:40px;
    padding:20px;
    border:1px solid #444;
  }

  #nav.open ul { display:flex; }

  #hamburger { display:block; }

  .hero h1 { font-size:3rem; }
}