The em unit

The em relative unit sets a font size of a child element based on the size of its parent. For example, a font equal to 2em means that it is twice the size of its parent.

Example

Let's give the text of the <p> element a font one and a half times larger than the font of its parent <div>:

html<div>
  text1
  <p>
    text2
  </p>
</div>

cssdiv {
  font-size: 14px;
}
p {
  font-size: 1.5em;
}

Результат:

See also