how know video is full screen website

/* example for "how know video is full screen website" */
video{
  height: 80vh
}
video:-webkit-full-screen{
  height: 80vh
}

video:-moz-full-screen{
  height: 80vh
}
video:-ms-fullscreen{
  height: 80vh
}

video:fullscreen{
  height: 80vh
}