Add scroll margin to anchor targets that need it

> scroll-pt-top on the body makes up for the sticky header exactly, and elements that want to have a little extra space can set scroll-mt to be used in addition.

> Nice addition. I think we can add them to other linkers as well like `details link`, `args link` etc which also provide hash links beside headers.

_Originally posted by @yathomasi in https://github.com/iterative/gatsby-theme-iterative/pull/140#discussion_r1035540691_

That PR added `scroll-margin` to docs headings, meaning that when navigated to via anchor (e.g. `href="#heading-id"`) the docs headings will have some extra space above them instead of hugging the navbar. This Issue tracks adding `scroll-margin` to other elements throughout the site that would benefit the same way.

Start by locating the existing scroll-margin behavior for documentation headings, then inspect the other hash-link providers mentioned in the issue, including details and args links. Apply the same anchor-spacing expectation to elements that need it and verify that navigation to their hash links leaves space below the sticky header.

Written by the indexing model from the issue text.