This figure illustrates the CSS "box model". You are looking at
three nested boxes: an outer box, a middle box, and an inner box.
All boxes are created by div elements. The inner box is nested
within the middle box, and the middle box, in turn, is nested
within the outer box. The inner box contains this text and has a
white background color (without which the maroon background of the
middle box would show through behind the text). This inner box has
no padding, border, or margin, which is why the text is immediately
adjacent to the top, bottom, and left side of its containing div.
The middle box contains the inner box as its content, which is
surrounded by 20 pixels of padding, a 20 pixel dashed silver
border, and a 20 pixel margin (in that order moving outward).
Note that the maroon background color of this middle box is the
background of the content and the padding and the border, but not
the margin. You can see that it's behind the border because the
border is dashed, but it's the yellow background color of the outer
box that shows under the margin of the middle box. As we already
said, this maroon background is also "behind" the inner box, but
you can't see it because of the white background of that inner box.
The outer box contains the middle box, with its content, padding,
border and margin as its own content, and also has a solid black
border 10 pixels wide and a yellow background color, but no padding
or margin. Note that the only "complete" box of the three (the only
one with all four of content, padding, border, and margin) is the
middle box. Make sure you identify all four parts of this box.