BOX 1 padding: 30px;
height: 300px;
width: 300px;
border: 10px solid #900;

BOX 2

padding: 30px;
height: 300px;
width: 300px;
border: 10px solid #900;
box-sizing:border-box;

BOX 3

padding: 30px;
height: 300px;
width: 300px;
border: 10px solid #900;
box-sizing:content-box;
/*Det er den der er standard*/