[FE] Adjust scaling of attachement field

[AnnaH3003]

Description

Currently, the drag and drop field for the attachements does not scale properly when resizing the browser window, making the UI look a bit off.

User story

1. As a user
2. I want / need the drag-and-drop field to look nice in every browser size
3. So that I don't get irritated when using the WebApp

Acceptance criteria

• the drag-and-drop field for attachements scales feasible when changing the size of the browser window

Definition of done (DoD)

• Work products are uploaded to the Github repository and merged to the main branch
• If necessary, the bill of materials section of the planning documents is updated
• Code/feature passes suited tests
• Code is peer-reviewed
• Help documentation (README) is updated
• Fits into our architecture, where possible

DoD general criteria

• Feature has been fully implemented
• Feature has been merged into the mainline
• All acceptance criteria were met
• Product owner approved features
• All tests are passing
• Developers agreed to release