[selectors] Fix example

Author: tabatkins

selectors/Overview.bs

@@ -1464,7 +1464,7 @@ Case-sensitivity</h3>
 	identifier <code>i</code> before the closing bracket (<code>]</code>).
 	When this flag is present, UAs must match the attribute's value
 	case-insensitively within the ASCII range.
-	Like the rest of Selectors syntax, 
+	Like the rest of Selectors syntax,
 	the <code>i</code> identifier is <a href="#case-sensitive">case-insensitive</a>
 	within the ASCII range.
 
@@ -2258,7 +2258,7 @@ The Selected-option Pseudo-class: '':checked''</h4>
 		An unchecked checkbox can be selected by using the negation
 		pseudo-class:
 
-		<pre>:not(:checked)</pre>
+		<pre>input[type=checkbox]:not(:checked)</pre>
 	</div>
 
 <h4 id="indeterminate">