Optimize code. Update templates.

src/components/Playground/templates/demo/App.tsx

@@ -0,0 +1,17 @@
+import { useState } from 'react'
+import './App.css'
+
+const App = () => {
+    const [count, setCount] = useState(0)
+
+    return (
+        <>
+            <h1>Hello World</h1>
+            <div className="card">
+                <button onClick={() => setCount((count) => count + 1)}>count is {count}</button>
+            </div>
+        </>
+    )
+}
+
+export default App