feat: Add automatic dropdown positioning

[MoritzWeber0]

Use the new anchor and position-try systems in CSS, available since January in all major browsers to automatically position the dropdown menu.

For horizontal positioning, automatically shift the dropdown menu to the left if there is not enough space on the screen. For vertical positioning, use scrolling to handle the overflow.

Resolves #1013

[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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[lenderom]

Hi @MoritzWeber0 thank you for your implemenation :)
Is there a way to hide the scrollbar in the menu?

(I guess it only appears on smaller screens)

[MoritzWeber0]

Hi @MoritzWeber0 thank you for your implemenation :) Is there a way to hide the scrollbar in the menu?

It should only appear if the scrollbar is necessary because the content overflows, which does happen on browser viewport with < 520px height. There are workarounds to hide scrollbars, but usually not really recommended as it also overwrites the system preferences regarding scrollbars. The default on Windows is to show the scrollbar, while on Android or macOS this isn't the case.