[css-align] Use more explicit terminology for the axis used by static-pos *-self. Fixes #1443.

Author: tabatkins

css-align/Overview.bs

@@ -1124,7 +1124,7 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 		<tr>
 			<th>'justify-self' Axis
 			<td>
-				The same axis that 'justify-self' corresponds to for in-flow children of the box's parent
+				The inline/row/main axis of the box's parent box.
 		<tr>
 			<th><a>Alignment Container</a>
 			<td>
@@ -1320,7 +1320,7 @@ Block/Cross-Axis Alignment: the 'align-self' property</h3>
 		<tr>
 			<th>'align-self' Axis
 			<td>
-				The same axis that 'align-self' corresponds to for in-flow children of the box's parent
+				The block/column/cross axis of the box's parent box.
 		<tr>
 			<th><a>Alignment Container</a>
 			<td>