Use non-null assertion

It's safer to use non-null assertions over unnecessary type assertions in TypeScript, since type assertions are bivariant.

-ReactDOM.createRoot(document.getElementById('root') as HTMLElement))
+ReactDOM.createRoot(document.getElementById('root')!)

Here are some practical advantages of using non-null assertions to render React elements:

• Readability of using the right syntax to assert a non-null value
• Discouraging use of as which many TypeScript beginners may not understand the dangers of
• You won't get a type error if you render to an Element that isn't an HTMLElement, such as <svg>/SVGSVGElement
• You will get a type error if you render to a value that isn't always an Element, such as Element | boolean