Border box

Width and height include padding and border.

What does box-sizing: border-box mean?

With border-box, the width you set includes padding and border, so a 300px card really is 300px wide.

.card { box-sizing: border-box; width: 300px; padding: 20px; }   /* still 300px wide */

Level: Apprentice · More CSS terms at this level

Updated September 27, 2026