[css-conditional-3] Fix markup, add test.

Author: fantasai

css-conditional-3/Overview.bs

@@ -493,6 +493,7 @@ as follows:
 	css-supports-040.xht
 	css-supports-041.xht
 	css-supports-042.xht
+	css-supports-046.xht
 	</wpt>
 
 The condition of the ''@supports'' rule
@@ -981,7 +982,7 @@ The following (non-editorial) changes were made to this specification since the
 <ul id="changes-20201208">
   <!-- to 6 Oct 2021 -->
   <li>Defined the terms [=CSS feature queries=] and [=supports queries=]
-      to refer to the conditional syntax of `@supports` rules,
+      to refer to the conditional syntax of the ''@supports'' rules,
       to allow better cross-referencing.
   <li>Removed the “unknown” value in [=CSS feature queries=]’ boolean logic,
       defining unrecognized syntaxes as “false” instead.