[css-values-5] Fix typos in early-resolution example (#12011)

Co-authored-by: Anders Hartvoll Ruud <andruud@google.com>

Author: andruud

css-values-5/Overview.bs

@@ -3480,7 +3480,7 @@ Argument Grammars and Spread Syntax</h3>
 		and only evaluates a single argument
 		matching the first successful test.
 
-		This allow ''if()'' to achieve behavior similar to `if` constructs
+		This allows ''if()'' to achieve behavior similar to `if` constructs
 		in other programming languages,
 		where later "branches" aren't evaluated at all
 		(beyond a basic parse)
@@ -3495,7 +3495,7 @@ Argument Grammars and Spread Syntax</h3>
 
 		<pre highlight=css>
 		.foo {
-			--color: if(media(width >= 600px): blue; else: var(--foo));
+			--color: if(media(width >= 600px): blue; else: var(--color));
 		}
 		</pre>
 	</div>