[Bug]: If a tooltip goes over text, the text overlaps the tooltip

**Describe the bug**

If a tooltip overlaps text in a document, the text itself (not the containers/element) is visible through the tooltip. See image below.

**To Reproduce**

Steps to reproduce the behavior:

1. Go to https://vanillaframework.io/docs/patterns/in-page-navigation
2. Make sure you are on large screen size
3. Hover over 'General Availability (GA) and variant Ubuntu...' to trigger the tooltip
4. Scroll the page so the tooltip overlaps text

**Screenshots**

**Additional context**

This only exists in a [PR](https://github.com/canonical/vanilla-framework/pull/5755) currently, if it is merged it will no longer be reproducible in the demo link provided

Start by reviewing PR #5755, which the issue says changes the demo behavior, then reproduce the tooltip overlap at the linked in-page navigation page on a large screen. Done means scrolling the tooltip over text no longer lets the text show through it.

Written by the indexing model from the issue text.