The width and height properties include the padding and border, but not the margin.
The width and height properties include the padding and border, but not the margin. This is the box model used by Internet Explorer when the document is in Quirks mode.
MDN
This is the default style as specified by the CSS standard.
This is the default style as specified by the CSS standard. The width and height properties are measured including only the content, but not the border, margin, or padding.
MDN
The box-sizing CSS property is used to alter the default CSS box model used to calculate widths and heights of elements. It is possible to use this property to emulate the behavior of browsers that do not correctly support the CSS box model specification.
MDN