USWDS - Bug: In-page navigation breaks for headings inside a USWDS alert component #6295

Describe the bug

The alert component creates a positioned container element (.usa-alert__body) that creates a new offset frame. The in-page navigation component then inserts an anchor inside the alert component. When clicking the link in the in-page navigation, it uses the anchor's offsetTop, which is the vertical distance between the selected element and its nearest offset parent. In this case, it's nearest offset parent is the alert container, not the page body itself.

Steps to reproduce the bug

1. Browse to https://handbook.tts.gsa.gov/tools/git-signing
2. Click About the cryptographic algorithm in the in-page nav
3. Note that the page scrolls to the top rather than to the linked heading

Expected Behavior

The browser should scroll to the selected heading, perhaps using getBoundingClientRect instead of offsetTop since the former computes absolute values (relative to the page, not any other elements in the tree).

Related code

https://github.com/uswds/uswds/blob/main/packages/usa-in-page-navigation/src/index.js#L202

Screenshots

No response

System setup

• USWDS version: 3.11.0
• All browsers

Additional context

Possibly related to:

• USWDS - Bug: In-Page Navigation scrolling does not work with Summary Box #5255

Code of Conduct

• I agree to follow this project's Code of Conduct.
• I checked the current issues for duplicate bug reports.