in class we are studying the box model which deals with four main parts of the box: the content, padding, border & margin.

content: the width & height of the content & images.
padding: space between the content and the border that is the same color as the background.
border: the border is in between the padding and margin can be be any color and any thickness.
margin: the “invisible” space between the border and other objects.

to figure out the entire width and height of an element you have to consider the dimensions of all four aspects. here’s a diagram…