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] {  /* TODO: implement */
    top: 0;
    width: auto;
    margin: 1em;
  }
}

._dialog_overlay {
  position: fixed;
  top: 0; right: 0; bottom: 0; left: 0;
}

dialog.fixed {
  position: fixed;
  top: 50%;
  transform: translate(0, -50%);
}