nav {
  position: sticky;
  top: 0;
  overflow: hidden;
  padding: 0.5em;
  border-bottom: 2px solid;
}

nav > div {
  float: left;
  min-height: 3em;
  text-align: center;
  overflow: hidden;
}

@media screen and (max-width: 500px) {
  nav {
    display: none;
  }
}