CSS Box Model: Width and Height of an Element

div {
  width: 320px;
  padding: 10px;
  border: 5px solid gray;
  margin: 0; 
}

//The total width of an element should be calculated like this:

// 320px (width)
// + 20px (left + right padding)
// + 10px (left + right border)
// + 0px (left + right margin)
// = 350px


// Total element height = height + top padding + bottom padding + top border 
//+ bottom border + top margin + bottom margin