[css-position-3] Percentages calculate against the original containing block. #5082

Author: fantasai

css-position-3/Overview.bs

@@ -869,6 +869,8 @@ Absolute Positioning Layout Model</h2>
 			Next, its width and height are resolved against this [=definite=] [=available space=],
 			as its [=preferred size=] capped by its [=maximum size=] (if any), floored by its [=minimum size=].
 			See [[#abspos-auto-size]].
+			Percentages, however,
+			are resolved against the original [=containing block=] size.
 
 		<li>
 			Then, the value of any ''margin/auto'' margins are calculated,