Steps to reproduce:

1. Server should be running
2. Switch to 'Dark' ('Dark high-contrast') theme
3. Go to 'Global view' dashboard
4. Check Server performance (Item value) widget

Result:
When 'Dark' or 'Dark high-contrast' theme is selected, color combination of background and text in Item value widget with Server performance data is not readable. Screenshots attached:

Expected:
As 'Global view' dashboard is set by default, color combination for dark themes should have more contrast between text and background in widgets those are already defined