[css-overflow-3] Handle non-start/start origins. #7237

Author: fantasai

css-overflow-3/Overview.bs

@@ -225,8 +225,8 @@ Scrollable Overflow</h3>
 		<li>
 			The border boxes
 			of all boxes for which it is the containing block
-			and whose border boxes are positioned not wholly outside
-			its <a>block-start</a> or <a>inline-start</a> padding edges,
+			and whose border boxes are positioned not wholly
+			in the [=negative scrollable overflow region=],
 			accounting for transforms by projecting each box onto
 			the plane of the element that establishes its <a>3D rendering context</a>.
 			[[!CSS3-TRANSFORMS]]