Calendar: Consider removing the hardcoded colors

[carolinan]

Description

The hard coded colors in the calendar block does not work well on some colored backgrounds or when the theme sets the link color to a light color.
The color contrast can be too low, making the texts difficult to read.

Related: #39053

Step-by-step reproduction instructions

1. In the editor, add a few default calendar blocks with default settings.
2. Place the blocks inside groups with different colored backgrounds to see potential contrast issues with the hard coded colors.

Screenshots, screen recording, code snippet

Here are two calendar blocks in Twenty Twenty-Two using the blue style variation:
The first is placed inside a group block with a white background, to mock light colored theme backgrounds:

Custom theme with dark grey background:

Environment info

WordPress 6.0 rc2, beta tester plugin
Current Gutenberg trunk

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

No

[t-hamano]

Hi @carolinan,

I'm interested in improving the style of the calendar block too.
I've made the following changes in try/block-calendar branch based on a table block (using the same table tag):

• Removed hard-coded colors
• Border color inherit text color
• Make thead bottom border thicker
• Add text and link color with block support

I would love to hear your opinions.

f2f1c83f9c7b6f1ba7bebd19ed0e25fe.mp4

[carolinan]

@t-hamano I have tried the branch. I like that it matches the table block better and that the table head background color was removed. Will you submit a PR?

[t-hamano]

Thanks for checking it out!
I created a PR #42029 based on this branch.
If you have any other suggestions, please comment on the PR.