This is a shorthand attribute for setting the width, style, and/or color of all four borders around an element in one assignment statement. Whichever attributes you don't explicitly set with this attribute assume their initial values. Numerous other attributes allow you to set the width, style, and color of individual edges or groups of edges, if you don't want all four edges to be the same.

Due to differences in the way browsers define their default behavior with regard to borders, every style sheet border rule should include the width and style settings. Failure to specify both attributes may result in the border not being seen in one browser or the other.