bug(datepicker): Header row cells have low color contrast ratio

[zarend]

Reproduction

Steps to reproduce:

1. Open the Datepicker Examples
2. Go to the “Basic date range picker” demo
3. Open the calendar dialog
4. Observe the contrast on the day of the week labels (S M T W T F S).

Expected Behavior

It should have a contrast ratio of at least 4.5:1.

Actual Behavior

It has a contrast ratio of 2.67.

Environment

OS| Browser |
ChromeOS | Google Chrome 91.0.4472.167 |
macOS Catalina | Google Chrome 91.0.4472.164 |
Windows 10 | Google Chrome 91.0.4472.106 |

Additional Notes

This is copied from an internal bug report found during a11y testing.

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