[css-logical] Clarify relationship of properties forming a logical property group. w3c#3033

Author: fantasai

css-logical-1/Overview.bs

@@ -295,12 +295,15 @@ Flow-Relative Box Model Properties</h2>
   that are <a>flow-relative</a> equivalents
   of <a>physical</a> box model properties.
   Each set of related flow-relative longhand properties
-  and their parallel physical properties
+  and their parallel physical properties,
+  which set equivalent styles on different sides or dimensions of a box,
   form a <dfn export>logical property group</dfn>.
   For example, the 'padding-*' properties
   form a single <a>logical property group</a>,
   the 'margin-*' properties
   form a separate <a>logical property group</a>,
+  the 'border-*-style' properties
+  form another <a>logical property group</a>,
   etc.
   The type of directional or axis mapping
   (<a>flow-relative</a> or <a>physical</a>)