fix: Use relative position for toc indicator during scroll on mobile

[MoritzWeber0]

No description provided.

[github-actions]

Hi there! 👋

Thank you for your contribution to the FIP Guide! 🚀
We appreciate your effort in making rail staff travel information more accessible. 🚄

Checklist before merging:

• Added a description to the Pull Request
• Checked the License of new pictures (non-commercial use without attribution)
• Modified content in English
• Modified content in German
• Modified content in French

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[MoritzWeber0]

@therobrob Do you have any idea why the indicator is cut-off in the light mode version, but not in the dark mode version?

There is a small white gap between the screen border and the indicator:

[therobrob]

Seems to work (although I doesn’t understand the mixin 100%)

[therobrob]

i think the small gap is present in light and dark mode. We have the border around the content-element, which is transparent in light mode. I've made it visible with this lightgreen color :)

[MoritzWeber0]

i think the small gap is present in light and dark mode. We have the border around the content-element, which is transparent in light mode. I've made it visible with this lightgreen color :)

Thanks! I removed the borders on the left & right on mobile to avoid the issue.
Also removed the mixin, it was too complex for what it was doing and replaced it with two simple CSS rules.