Once you move Black Keys Resource Pack into your active list, it replaces several normal screens beyond the initial start menu. You can quickly inspect both title and in-world interfaces to confirm every dark surface applied properly.
Checking the Start Screen
1. Return to the main title screen after clicking Done in Options > Resource Packs.
2. Inspect the main menu buttons—they should now display a solid black color with easy-to-read button text instead of the standard gray stone look.
3. Check behind the buttons to confirm the default menu background has been replaced with the matching dark theme.
Checking In-Game Menus
1. Load into a world and press your inventory key (E by default) to view the dark-themed inventory screen around your items and tools.
2. If you have access to Creative mode, open the creative inventory menu to confirm the dark theme covers the tabs for building blocks and tools.
3. Press your advancements key (L by default) to open the advancements screen and verify that the background behind your progress tracker is dark as well.