Hi tuanphan, I'm having the same issues - lots of dead space in the header section on most of my webpages, but only on mobile. I've tried all the CSS you've provided (except for the gallery view) but nothing works. Any ideas?
www.TheMcGuireMethod.com
Pages in screenshots:
https://themcguiremethod.com/present-like-a-pro-pre-sale
https://themcguiremethod.com/the-method