[css-position-3] Fix cross-ref

Author: frivoal

css-position-3/Overview.bs

@@ -671,17 +671,17 @@ Absolute Positioning</h3>
 	If both [=inset properties=] in a given axis are ''top/auto'', then,
 	depending on the box’s [=self-alignment property=] in the relevant axis:
 	<dl class=switch>
-		<dt>for ''align-self/self-start'' alignment or its equivalent
+		<dt>for ''<self-position>/self-start'' alignment or its equivalent
 		<dd>
 			Set its start-edge [=inset property=] to the static position,
 			and its end-edge [=inset property=] to zero.
 
-		<dt>for ''align-self/self-end'' alignment or its equivalent
+		<dt>for ''<self-position>/self-end'' alignment or its equivalent
 		<dd>
 			Set its end-edge [=inset property=] to the static position,
 			and its start-edge [=inset property=]  to zero.
 
-		<dt>for ''align-self/center'' alignment
+		<dt>for ''<self-position>/center'' alignment
 		<dd>
 			Let <var>start distance</var> be the distance from
 			the center of its [=static position rectangle=]