dialog 
  position: absolute
  left: 0
  right: 0
  width: -moz-fit-content
  width: -webkit-fit-content
  width: fit-content
  height: -moz-fit-content
  height: -webkit-fit-content
  height: fit-content
  margin: auto
  border: solid
  padding: 1em
  background: white
  color: black
  display: none

dialog[open] 
  display: block

dialog + .backdrop 
  position: fixed
  top: 0
  right: 0
  bottom: 0
  left: 0
  background: rgba(0,0,0,0.1)

/* for small devices, modal dialogs go full-screen */
@media screen and (max-width: 540px) 
  dialog[_polyfill_modal]
    top: 0
    width: auto
    margin: 1em