General: Reduce visual noise in header buttons

[Bofan-Zhu]

Checklist

General

• I tested all changes and their related features with all corresponding user types.
• I chose a title conforming to the naming conventions for pull requests.

Motivation and Context

Currently, the buttons in the header visually clash too much with buttons in the content areas. To reduce this visual noise and we are transforming the header buttons to text buttons.

Description

This PR:

• changes the header buttons to use variant "text"
• reduces the width of the buttons
• adds a "divider" between the buttons to visually separate both

Steps for Testing

Prerequisites:

1. Navigate to TumApply and view the header
2. Check that visual noise is reduced and buttons are still visually detached from each other

Review Progress

Code Review

• Code Review 1

Manual Tests

• Test 1

Screenshots

Before:

Now:

[sachmii]

Looks great, thank you!

[Abi107717]

Tested locally and Code LGTM as well, thank you 😊