Fix scrollbar appearing behind sticky header

Description

The scrollbar can end up unreachable behind a sticky header if the page is long enough on an issue.

Steps to reproduce

1. Open an issue with a long description
2. Scroll down the page
3. Observe the scrollbar position relative to the sticky header

Expected behavior

The scrollbar should remain accessible and not be hidden behind the sticky header.

Actual behavior

The scrollbar appears behind the sticky header, making it unreachable.

Screenshots

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