How to make this look better on mobile etc

Hello,
I was sad to realize this theme (Holidayshop) looks pretty yucky on mobile. Is there a way I can have the main image scale better for mobile or any other suggestions?

I would also like to know how I would go about making the main image dynamic like on this page: https://www.morrisessex.com/

I would like the logo and nav menu to aight to the top of the banner image – I have been trying to do this with the flex property with no luck – any tips?

Thanks!

The page I need help with: [log in to see the link]