Check out example codes for "video is full screen". It will help you in understanding the concepts better.

Code Example 1

/* 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
}

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