Using Picture element on header image

I can use WP to insert the home page’s top header image, but I’d like to modify it with CSS (to swap out different pictures to fit narrower screen widths). I would put the CSS in Appearance > Customize > Additional CSS.

How do I reference the header image?

I’m using Twenty Ten. Will the Additional CSS pane be removed if the site is upgraded or changed from Twenty Ten?

you can make your header in elementor , you can customize it as you want

Thanks! Looks very good.