Improve theme color consistency for trees and tables

The theme colors for output tables (XY output tree, data tree and events table) should be made consistent (header foreground and background, hover and selection background, gridlines, etc.)

Start with the theme and rendering entry points for the XY output tree, data tree, and events table, then compare how each defines header, hover, selection, and gridline colors. Identify the existing theme values used by all three components and confirm that the resulting tables and trees present consistent colors in each state.

Written by the indexing model from the issue text.