Mobile menu always on with sticky header

Hi all,

Site: https://cluster4.website-staging.uk/simplyfloors.co.uk/

Is there a way to have the mobile/collapsed/burger (whatever you want to call it) menu always on, regardless of viewport size, when the sticky header is active (i.e. when you scroll down the page)?

That is to say, I’d like the expanded menu to show still when at the very top of the page.

I’ve been looking around and couldn’t see anything answering this question.

Thanks in advance.