fixing typo

Author: howcom

css3-gcpm/Overview.src.html

@@ -2743,7 +2743,7 @@ <h2>Page and column floats, alternative syntax</h2>
 <dl>
 
 <dt>left, right, top, bottom
-<dd>relative to physical screen
+<dd>relative to physical viewport
 
 <dt>line-left, line-right
 <dd>relative to inline axis