#backdrop {
  position: fixed;
  top: 0;
  left: 0;

  width: 100vw;
  height: 100vh;
  opacity: 0;
  transition: opacity 5000ms ease-in-out;
  z-index: -1;
  pointer-events: none;
}

html[data-theme="story"] #backdrop {
  opacity: 1;
}

html[data-theme="notstory"] #backdrop {
  opacity: 0.5;
}