CSS Studio

With content-box, width is only the content. Padding and border are added outside it, so the element grows. border-box keeps width fixed and shrinks the content instead.

Does CSS width include padding?

Only with box-sizing: border-box. The default, content-box, means width is the content area. Padding and border sit outside that width.

What is the difference between margin and padding?

Padding is space inside the border, around the content. Margin is space outside the border, between this element and its neighbors. Margin does not take background color.