[css-grid-3] Tweak wording and expand note about dense packing empty spaces.

Author: fantasai

css-grid-3/Overview.bs

@@ -869,7 +869,7 @@ Grid Lanes Layout and Placement Algorithm</h3>
 
 		<li>
 			If the [=grid lanes container=] uses ''item-pack/dense'' packing,
-			and there exists skipped empty space in the layout
+			and there exists skipped spaces in the layout
 			(e.g. due to spanning items)
 			into which the item, as it is sized now,
 			could have fit if it were placed earlier,
@@ -881,11 +881,11 @@ Grid Lanes Layout and Placement Algorithm</h3>
 			Rewind the [=auto-placement cursor=] and the [=running position=]
 			to their values before this item’s placement.
 
-			Items that <em>visually</em> intrude into preceding empty spaces
+			Note: Items that <em>visually</em> intrude into preceding empty spaces
 			(via negative margins, ''position: relative'', transforms, etc.),
 			do not affect the size of those empty spaces.
-			<span class=note>Later items might get placed in those spaces
-			and visually overlap these previous items.</span>
+			Later items can get placed in those spaces
+			and visually overlap these previous items.
 
 			Note: Dense packing both ignores the [=auto-placement cursor=] when backfilling,
 			and does not update it after placement.