Make 'Now' button on DateTime widget consistent with 'Add' button on List widget

[taineriley1]

Summary

Closes #5706
Changed the styling of the 'Now' button on the DateTime widget to match the styling of the 'Add xxx' button on the List widget.

Test plan
Tested locally

Figure: 'Now' button changed to be consistent with 'Add xxx' buttons

Checklist

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[erezrokah]

Thanks @taineriley1 🎸