em is an HTML element that set a strong emphasis on words of a sentence.
If you want to add an extra comment (extra voice) on the actual text, you may want to use the idiomatic element instead.
The default font styling is italic and should have been bold instead to make a strong difference with the the idiomatic element
This is <em>not</em> what I intended to do
<p><em>Cats are cute animals!</em></p>