box-sizing.md

box-sizing: border-box;

The CSS box-sizing property allows us to include the padding and border in an element's total width and height.

By default, the width and height of an element is calculated like this:

width + padding + border = actual width of an element

height + padding + border = actual height of an element

This means: When you set the width/height of an element, the element often appears bigger than you have set (because the element's border and padding are added to the element's specified width/height).

The property box-sizing can have 2 values: content-box and border-box:

• content-box gives you the default CSS box-sizing behavior. If you set an element's width to 100 pixels, then the element's content box will be 100 pixels wide, and the width of any border or padding will be added to the final rendered width, making the element wider than 100px.

• border-box tells the browser to account for any border and padding in the values you specify for an element's width and height. If you set an element's width to 100 pixels, that 100 pixels will include any border or padding you added, and the content box will shrink to absorb that extra width. This typically makes it much easier to size elements.