height is how tall a tool player is, in whole pixels. Anything else, such as 30rem or 50%, is ignored and the player keeps its default height.
Incorrect
::embed{url="https://codepen.io/onmax/pen/abcdEF" title="The duck pond counter" height="30rem"}
::Correct
::embed{url="https://codepen.io/onmax/pen/abcdEF" title="The duck pond counter" height=480}
::