[BUG] Modal closeButton and supplementaryButton too small

[RasmusKjeldgaard]

• I have written a good issue

Describe the bug

After #2245 was implemented, it seems that the modal buttons where not updated to the correct size.
It should be size md according to zeplin: https://zpl.io/z89qQl7.

Describe how to reproduce the bug

Replace this with steps to reproduce the behavior:

1. Go to https://cookbook.kirby.design/#/home/showcase/modal
2. Click on 'show modal' button

Which Kirby version was used?

6.0.1

---

Checklist:

The following tasks should be carried out in sequence in order to follow the process of contributing correctly.

Verification

To make sure the bug is not intended behaviour; it should be verified by a member of team Kirby before moving on to implementation.

• Make sure the NOT verified label has been removed by a member of team Kirby; do not proceed until this is done

Implementation

The contributor who wants to implement this issue should:

• Make sure you have read: "Before you get coding".
• Signal to others you are working on the issue by assigning yourself.
• Create a branch from the develop branch following our branch naming convention.
• Create a test that reproduces the bug following guidelines in: "The good: Test".
• Write code to fix the bug

Review

Once the issue has been implemented and is ready for review:

• Do a self-review.
• Create a pull-request.