Jumping to anchor within modal with a fixed header

Hi all,
I am having a bit of a problem.
I have a script that is for nested modals, that when a link is clicked it jumps straight to an anchor. It works fine.
However when styling, I would like to have a fixed header as the ".content" div scrolls to the anchor.
When ".content" has a height of 80vh it looks fine, but the script doesn't scroll to the anchor.
When ".content" has a height of 80% the script works, but the fixed header doesn't stay fixed and scrolls with the ".content".
How can I...

Jumping to anchor within modal with a fixed header

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