Summary:
The background on the left side of the trading GUI is not retextured in the Adventure Time, Star Wars, and Steven Universe resource packs, unlike the background in the loom, stonecutter, recipe book, and Creative inventory.

Steps to Reproduce:

1. Open a world with the Adventure Time, Star Wars, or Steven Universe resource pack enabled
2. Spawn a villager or wandering trader
3. Open the trading GUI
4. Look at the background on the left side

Observed Results:
The background uses the default gray texture.

Expected Results:
The background should use the same texture as the background in the loom, stonecutter, recipe book, and Creative inventory.

Screenshots: