fix: classList example

src/routes/concepts/components/class-style.mdx

@@ -85,7 +85,7 @@ When the value is `true`, the class is applied; when `false`, it is removed.
 const [current, setCurrent] = createSignal("foo");
 
 <button
-	classList={current() === "foo" ? "selected" : ""}
+	classList={{ "selected" : current() === "foo" }}
 	onClick={() => setCurrent("foo")}
 >
 	foo