Tile Palette: "Create New Tilemap" dropdown area is displayed in several colors

Steps to reproduce:

1. Create a project using the Universal 2D template
2. Go to "Window" -> "2D" -> "Tile Palette"
3. Find and select the "Create New Tilemap" dropdown
4. Click "Create New Tilemap" and select any item from the list
5. Select and expand the same dropdown
6. Observe the UI

Actual results: Area before the selected tilemap is displayed in a different background color

Expected results: All the background should be in the same color

Reproducible with versions: 6000.0.63f1, 6000.2.15f1, 6000.3.1f1, 6000.4.0a5, 6000.5.0a3

Tested on (OS): macOS - Tahoe 26.1