Restructure code

src/ui/App.css

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+.App {
+  text-align: center;
+}
+
+.App-logo {
+  height: 40vmin;
+  pointer-events: none;
+}
+
+@media (prefers-reduced-motion: no-preference) {
+  .App-logo {
+    animation: App-logo-spin infinite 20s linear;
+  }
+}
+
+.App-header {
+  background-color: #282c34;
+  min-height: 100vh;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  font-size: calc(10px + 2vmin);
+  color: white;
+}
+
+.App-link {
+  color: #61dafb;
+}
+
+@keyframes App-logo-spin {
+  from {
+    transform: rotate(0deg);
+  }
+  to {
+    transform: rotate(360deg);
+  }
+}

src/ui/App.test.tsx

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+import React from 'react';
+import { render, screen } from '@testing-library/react';
+import App from './App';
+
+test('renders learn react link', () => {
+  render(<App />);
+  const linkElement = screen.getByText(/learn react/i);
+  expect(linkElement).toBeInTheDocument();
+});

src/ui/App.tsx

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+import React from 'react';
+import logo from './logo.svg';
+import './App.css';
+
+function buttonFunctionality() {
+  alert('Button clicked!');
+}
+
+function App() {
+  return (
+    <div className="App">
+      <button onClick={buttonFunctionality}>Cool button</button>
+    </div>
+  );
+}
+
+export default App;