[css-scoping-2][editorial] Fix typo: it's -> its (#6568)

Author: Kaleidea

css-scoping-2/Overview.bs

@@ -124,13 +124,13 @@ Scoped Styles</h2>
 		</pre>
 	</div>
 
-	Each resulting [=scope=] includes a [=scoping root=] and all it's descendants,
+	Each resulting [=scope=] includes a [=scoping root=] and all its descendants,
 	up to and including any [=scope boundary=] elements,
 	but not the descendants of those boundaries.
 
 	In contrast to <a href="#shadow-dom">Shadow Encapsulation</a>,
 	which describes a persistent one-to-one relationship in the DOM
-	between a [=shadow host=] and it's nested [=shadow tree=],
+	between a [=shadow host=] and its nested [=shadow tree=],
 	multiple overlapping [=scopes=] can be defined in relation to the same elements.
 
 	<div class=example>