The % unit

The % relative unit sets a size of a child element relative to the size of its parent. For example, the width of a rectangle equal to 50% means that it is half the size of its parent.

Example

Let's give the child element's rectangle a width of 20% and a height of 40%:

html<div>
  <p></p>
</div>

cssdiv {
  border: 1px solid black;
  width: 200px;
  height: 100px;
}
p {
  border: 1px solid red;
  width: 20%;
  height: 40%;
}

Результат:

See also