[css-position-3] Use the original (not grid-modified/anchor-modified) containing block for alignment safety. #10316

Author: fantasai

css-position-3/Overview.bs

@@ -908,7 +908,7 @@ Absolute Positioning Layout Model</h2>
 			the box aligns at an "in-between" level of safety:
 			it is ''unsafe''-aligned within its [=inset-modified containing block=],
 			but shifted, if necessary, to not overflow
-			the union of its [=absolute-position containing block=] and its [=inset-modified containing block=]--
+			the union of its [=original containing block=] and its [=inset-modified containing block=]--
 			unless it is larger than that rectangle, in which case it is start-aligned to it.
 	</ol>