em tag in html

1i has the purpose of presenting something in italicised style.
2em has the purpose of giving emphasis to the content.
3
4In practice emphasised content is typically displayed italicised,
5so the difference on the face of it is non-existing from a
6presentation standpoint. However, emphasis is semantic while
7italics is presentation.

1<em>this is how to emphasis</em>

1basically italic
2<p>You <em>have</em> to hurry up!</p>

1
2    em { 
3  font-style: italic;
4}