On a date- picker page (ie, Tasks > Cloud Sync Tasks > Schedule the CS Task > Custom), all fields should be visible in all themes. Check especially the high contrast theme. Also the calendar itself should fit within the space allotted for it (although it still sometimes shows irregular row height on Firefox)
See circled areas in screenshot:
- in 'high contrast' theme, the 'preset' popup text is, well, not high contrast.
- sometimes circles around dates are drawn as ovals
- for months with many weeks, a line is drawn through the dates of the last week.