[BUG]Calendar component - higher contrast between disabled and enabled dates

[alxzak]

• [x] I have written a good issue

Describe the bug

The contrast between the disabled and the enabled dates in the calender are not high enough.

Describe how to reproduce the bug

Which Kirby version was used?

## What was the expected behavior?

Add any screenshots

Please complete the following information:

• OS: [e.g. Windows, MacOS, iOS]
• Browser [e.g. Chrome, Safari]
• Browser version [e.g. 22]

Are there any additional context?

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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.

[jkaltoft]

@alxzak @henrikvoetmand

Can you specify the desired colors?