How to make <div> height responsive?

[solidcodes]

Hi guys,

I have a <div> tag and the CSS properties are below,

#header{ 
	background-color:#333;
	height:150px;
}

So how to make this responsive?

Thank you very much in advanced.

[solidcodes]

I think I solved the problem.

The solution,

#header{ 
	background-color:#333;
	width: 100%;
	height: 20%;
}

[markbrown4]

No, the right answer is:

A div is display: block by default so will be 100% wide.
If you don't set a height then it will be the height of it's contents.
You need no styles at all to make a div responsive