Web Renderer: Clarify stacking context

[JonnyBurger]

<div style={{backgroundColor: '#e0e0e0', position: 'relative'}}>
	<div
		style={{
			position: 'absolute',
			top: 5,
			left: 5,
			fontSize: 12,
			fontWeight: 'bold',
		}}
	>
		scale-down
	</div>
	<Img
		src={staticFile('1.webp')}
		style={{
			width: '100%',
			height: '100%',
			objectFit: 'scale-down',
		}}
	/>
</div>

The web will render the text on top of the image, but Remotion renderer will render the text first and then the image.
We don't necessarily have to implement this, but it should be documented.