feat(styles): add delta theming for Calendar [ci visual]

[mikerodonnell89]

part of #3213

BREAKING CHANGE

• year & month items should have fd-button fd-button--transparent classes from now.

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[InnaAtanasova]

1. The border/box-shadow is not rounded (Horizon):

2. The years and months are blue in the design specs and the current month and year are blue and bold:

Fundamental-styles:

[mikerodonnell89]

@InnaAtanasova re: corners without border-radius, that is coming from the dialog

re: the blue buttons, I am waiting on the button PR before that

[github-actions]

This pull request is stale because it has been open 2 days with no activity. Remove stale label or comment or this will be closed in 3 days

[platon-rov]

@InnaAtanasova yours feedback processed now.

However, the year & month items still will have black color in horizon themes and it's because of the bug we have on main. It's already fixed in button's pr and will be applied automatically here also, so you can just skip this one.

[InnaAtanasova]

The week days and number of the week should not have background

[github-actions]

This pull request is stale because it has been open 2 days with no activity. Remove stale label or comment or this will be closed in 3 days