Merge pull request #1 from zhangenming/zhangenming-patch-box3

[css-box-3] added description, be consistent with margin.

Author: zhangenming

css-box-3/Overview.bs

@@ -428,7 +428,9 @@ Padding Shorthand: the 'padding' property {#padding-shorthand}
 	the top is set to the first value,
 	the left and right are set to the second,
 	and the bottom is set to the third.
-
+	If there are four values
+	they apply to the top, right, bottom, and left, respectively.
+	
 	<div class="example">
 		The following code demonstrates some possible 'padding' declarations.