How to add a smooth animation for the header slide-up on mobile

Store Design
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Hi, how can I add a smoother slide-up animation for the header on mobile? Right now, I have the basic one from Shopify by default, and sometimes it opens with a slight slide-up, but it’s about 50/50 whether it works.

I’d like to add the same or a similar animation as on this store: https://tomnoske.store/

And here’s my store: https://1049xn-ya.myshopify.com/

I only need this for mobile.

Thanks a lot, I really appreciate your help!
Tim