[css-variables-1] Fix some linking warnings.

Author: tabatkins

css-variables-1/Overview.bs

@@ -19,6 +19,8 @@ Default Highlight: css
 
 <pre class=link-defaults>
 spec:css-syntax-3; type:dfn; text:identifier
+spec:css-color-3; type:property; text:color
+spec:selectors-4; type:selector; text: :lang()
 </pre>
 
 <h2 id="intro">
@@ -130,7 +132,9 @@ Defining Custom Properties: the '--*' family of properties</h2>
 	</div>
 
 	Unlike other CSS properties,
-	custom property names are <a>case-sensitive</a>.
+	custom property names are <em>not</em> [=ASCII case-insensitive=].
+	Instead, custom property names are only equal to each other
+	if they are [=identical to=] each other.
 
 	<div class='example'>
 		While both '--foo' and --FOO are valid,