Masthead image resize on iPhone, etc

I remember seeing a youtube video instruction for creating a background image for the masthead or top pallet that will resize when on iPhone or such. Last one I made didn’t resize and the title would move over on to the image. Can you please send me the link.
Thanks

could it be this one from @Matthew 's YouTube page?

Looks like it!

Some things will no doubt be different since it was made back in the BL 1 days