The warning button used in dialogs is not affected by the "High Contrast" resource pack

The High Contrast resource pack is intended to make all UI elements have a…well, higher contrast. While most buttons and icons do indeed use a high contrast texture, the warning button used in dialogs doesn’t, making it inconsistent.

Steps to reproduce:

1. Activate the High Contrast resource pack, either directly from the Resource Packs menu or via the option in Accessibility Settings.

2. Open any dialog (e.g. by running the command /dialog show @s minecraft:custom_options, which opens a vanilla dialog that by default is empty).

3. Observe the warning button near the top of the screen, both in its selected and unselected states.

Expected result:

The warning button is changed by the High Contrast resource pack.

Actual result:

The warning button is not affected by the High Contrast resource pack.