Add placeholder text to dashboard theme

[FWW]

Currently, placeholder text is not customisable for Category Selector, Number Selector, or Date Selector when added to a header in the dashboard.

As the placeholder text for these items is set to a light grey it means that any foreground colour that is dark or of a similar colour makes the placeholder text almost impossible to read. If someone had a corporate colour matching this placeholder hex, it would be invisible with no ability to customise.

Setting the theme / custom theme text colours all to white do not change the placeholder text.

[SandraLuken1]

This was fixed with the February 2025 ArcGIS Online update. The placeholder text for the date selector  will now respect the text color of either the theme or the side panel.