[css-cascade-6] Fix link errors, etc (w3c#8467)

Author: andruud

css-cascade-6/Overview.bs

@@ -26,6 +26,7 @@ spec:css-values-3; type: value; text:ex
 spec:css-conditional-3; type:at-rule; text:@media
 spec:mediaqueries-4; type:type; for:@media; text:all
 spec:mediaqueries-4; type:type; text:<media-query>
+spec:selectors-4; type:dfn; text:subject
 </pre>
 
 <pre class=ignored-specs>
@@ -377,7 +378,7 @@ Scoping Styles: the ''@scope'' rule</h4>
 
 	[=Pseudo-elements=] cannot be [=scoping roots=] or [=scoping limits=];
 	they are invalid both within <<scope-start>> and <<scope-end>>.
-  
+
 	A ''@scope'' rule which does not specify a <<scope-start>>
 	produces a single <dfn>implicit scope</dfn> as follows:
 
@@ -531,7 +532,7 @@ Scoped Descendant Combinator</h4>
 	This combinator differs from the [=descendant combinator=]
 	in that it applies [=weak scoping proximity=]
 	to the relationship between <css>A</css> and <css>B</css>.
-	It does not change the [=:scope element=].
+	It does not change the '':scope'' element.
 
 	ISSUE: Should the [=scoped descendant combinator=]
 	use strong or weak scoping proximity?