vmax and vmin fallback technique

fallback.css

@media (orientation: portrait) {
  .width-vmax { width: 100vh }
  .width-vmin { width: 100vw }
  .height-vmax { height: 100vh }
  .height-vmin { height: 100vw }
}

@media (orientation: landscape) {
  .width-vmax { width: 100vw }
  .width-vmin { width: 100vh }
  .height-vmax { height: 100vw }
  .height-vmin { height: 100vh }
}