section {
  position: absolute;
  width: 100vw;
  height: 100vh;
  display: none;
  place-content: center;
  margin-top:0px;
  margin-bottom:0px;
}

@media (max-height:700px) {
   section {
      height:600px;
      min-height: 100vh;
   }
}

nav {
  position: fixed;
  z-index: 999;
  top: 0;
}

.up {
  animation: up 300ms;
  display: grid;
}

@keyframes up {
  from {
    transform: translateY(100dvh)
  }
  to {
    transform: translateY(0)
  }
}

.down {
  animation: down 300ms;
  display: grid;
}

@keyframes down {
  from {
    transform: translateY(-100dvh)
  }
  to {
    transform: translateY(0)
  }
}