Selection boxes of plain messages within dialogs don’t render with black backgrounds

The Bug:

Selection boxes of plain messages within dialogs don’t render with black backgrounds.

Throughout the game, when a piece of text is selected, it normally renders with a black background, however, this isn’t the case for plain messages within dialogs.

Steps to Reproduce:

1. Display a dialog with a plain message by using the command provided below.

   /dialog show @s {"type":"minecraft:notice","title":"MC-299874","body":{"type":"minecraft:plain_message","contents":"Click Me - I don't have a background."}}

2. Click on the plain message and observe that the selection box doesn’t render with a black background.

Observed Behavior:

Selection boxes don’t render with black backgrounds.

Expected Behavior:

Selection boxes would render with black backgrounds.