css padding issue

[divinedesigns1]

can someone tell me why everytime i add padding to a div with a width of say 100% or 80% the div expand....i thought padding was suppose to be for within the div and not suppose to expand that div or element.

[Ingolme]

That means you don't understand the box model. Here's an explanation: http://www.w3schools.com/css/css_boxmodel.asp

 

You can change the way the box model works using the box-sizing property, it's supported in Internet Explorer 9 and above. If you need to support Internet Explorer 8 you will have to use the classic box model.