Merging layout from item page from theme "a" to theme "b"

Hey folks,

i am not quite sure if this is the right category to ask this question but i am wondering if it is possible to “merge” themes.
My Usecase:
I have theme “a” which i really like for the collection page and theme “b” which i really like for the item page. Both have a different structure different headers, footers etc. which would make it hard only adjusting the css files.
So my question is can I somehow make the theme that appears depending on which page is viewed? something like if on item level page use /theme/“a”/show …

If not what would you suggest would be the best way to achieve my goal to merge the page from one theme to another theme?

It’s technically possible to change the theme shown for different pages… I wouldn’t really recommend it, though.

What do you really like about the one vs. the other? It should be possible to basically apply the parts you like from the one page into the other theme you otherwise like—but it’ll take some editing of the theme to accomplish that.

Hey, yeah i noticed that. I like the minimalist design but on item level i would prefer the big picture one. So thats a problem, cause integration is pretty huge. There is a lot to do and i think i got very far right now, to adjust everything and copy the js files etc so the page looks fine. Biggest problem right now is to adjust the header, which doesnt seem to work when i try to get the one from big picture working. the search option is not working right now, think i am missing something here.
And i have to adjust the stylesheet that it looks fine on mobile aswell which seems to be troubling aswell.