Add header and footer to WP backend

hi,
In order to look less ‘wp feel’, I want to add a header in the backstage in order to look more blend in like the frontend. Nothing much I want to add, just the header and footer is enough. The content section remains the original style.

But I can’t find an appropriate hook to this area. I tried to add get_header(); into wp-admin/admin-header.php and it works. However, I don’t want to mess up with wp core files, so is there any way to add the files?