[css-backgrounds-4] Logical background-position properties do not have initial values.

This resolves the removed issue, as agreed about three or four minutes
ago in the WG meeting.

Author: dbaron

css-backgrounds-4/Overview.bs

@@ -86,8 +86,6 @@ Background Positioning Longhands: the 'background-position-x', 'background-posit
 
 	Issue: This section is still being worked out. The tricky thing is making all the start/end keywords work sanely.
 
-	Issue: Initial values are incompatible.
-
 	<pre class='propdef'>
 		Name: background-position-x
 		Value: [ center | [ left | right | x-start | x-end ] [ <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]? ]#
@@ -117,7 +115,7 @@ Background Positioning Longhands: the 'background-position-x', 'background-posit
 	<pre class='propdef'>
 		Name: background-position-inline
 		Value: [ center | [ start | end ] [ <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]? ]#
-		Initial: start
+		Initial: not applicable (initial value comes from physical property)
 		Applies to: all
 		Inherited: no
 		Percentages: refer to inline-size of background positioning area <em>minus</em> inline-size of background image
@@ -130,7 +128,7 @@ Background Positioning Longhands: the 'background-position-x', 'background-posit
 	<pre class='propdef'>
 		Name: background-position-block
 		Value: [ center | [ start | end ] [ <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]? ]#
-		Initial: start
+		Initial: not applicable (initial value comes from physical property)
 		Applies to: all
 		Inherited: no
 		Percentages: refer to size of background positioning area <em>minus</em> size of background image