#nav {
  transition: background-color 3.5s;
  background-color: gray;
}
[popover]:popover-open {
  opacity: 1;
  transform: scaleX(1);
  @starting-style {
    opacity: 0;
    transform: scaleX(0);
  }
}
#target {
  transition: background-color 1.5s;
  background-color: green;
}
@starting-style {
  #target {
    background-color: transparent;
  }
}
#source {
  transition: background-color 2.5s;
  background-color: red;
}
source:first {
  opacity: 1;
  transform: scaleX(1);
  @starting-style {
    opacity: 0;
    transform: scaleX(0);
  }
}
#footer {
  color: yellow;
}
@starting-style {
  #footer {
    background-color: transparent;
  }
}
nav > [popover]:popover-open {
  opacity: 1;
  transform: scaleX(1);
  @starting-style {
    padding: 10px 8px 6px 4px;
  }
}
aside > [popover]:popover-open {
  opacity: 1;
  transform: scaleX(1);
  @starting-style {
    padding: 10px 20px 30px 40px;
  }
}
