Box Model
This box has a border and padding. The width and height have not
been set to anything in particular, so the box will be as wide as
the page, and as high as needed to to hold the text. That I'm trying
to make verbose enough to take up some space, and make the padding
evident.
This box has some more specific sizes, and a bit of left margin,
which makes it appear shifted to the right. And rounded
corners on the right.
This is the first inner box. It is a as wide as its container,
and 3/10s of its height.
This is the second inner box. It is wider than its container,
since its 100% size does not include its border. It is therefore
too wide by twice the border width, and sticks out to the right.
This is the third inner box. It's width is its container
by default, and its height is set for the remaining 4/10.
But that's too much because the second box is too high. The
background shows through the right margin, but not the left padding.