HTML and CSS Reference
Figure1-2.Box model details
An inline-level box in CSS generates one or more rectangular boxes called inlineboxes, de-
pending on whether the inline box is broken across multiple lines. The following rules apply
to inline box:
▪ For the properties left , right , top , bottom , margin-left , margin-right , margin-top ,
and margin-bottom , any value of auto is converted to 0 (zero).
▪ width and height do not apply to nonreplaced inline boxes.
▪ For replaced inline boxes, the following rules apply:
— If height and width are both auto and the element has an intrinsic width (e.g., an im-
age), that value of width is equal to the element's intrinsic width. The same holds true for
— If height and width are both auto and the element does not have an intrinsic width but
does have an intrinsic height and layout ratio, then width is set to be the intrinsic height
times the ratio.
— If height and width are both auto and the element does not have an intrinsic height
but does have an intrinsic width and layout ratio, then height is set to be the intrinsic
width divided by the ratio.
There are a few rules even more obscure than those last two, which are too lengthy to include
here; see http://w3.org/TR/css3-box/#inline-replaced for details.