Home page header flashes when scrolled to a certain position

# Bug Report

## Prerequisites

* [ ] Can you reproduce the problem on TYPO3 v11.5 LTS
* [ ] Can you reproduce the problem on TYPO3 v12.4 LTS
* [x] Did you [perform a cursory search](https://github.com/issues?q=is%3Aissue+user%3Abenjaminkott+repo%3Abenjaminkott%2Fbootstrap_package)
to see if your bug or enhancement is already reported?

## Description

When slowly scrolling on [bootstrap-package.com](https://www.bootstrap-package.com/) the page header starts flashing. See attached screen recording.

## Steps to Reproduce

1. Open [bootstrap-package.com](https://www.bootstrap-package.com/)
2. Slowly scroll down
3. See strobe effect

### Expected behavior

The animation should probably be started at the starting pixel threshold and not be constrained to the current scroll position.

### Actual behavior

The animation is constrained to the scroll position which causes the page header to flicker.

### Screenshots

https://github.com/benjaminkott/bootstrap_package/assets/25110308/99b3b319-437d-42d6-9ce9-b64a048ccd0d

## Versions

https://www.bootstrap-package.com/

Start at the bootstrap-package.com home page and reproduce the flashing by slowly scrolling through the header transition. Trace the header's scroll animation and identify the threshold behavior; done means the header no longer flickers when scrolling slowly through that position.

Written by the indexing model from the issue text.