If you use another resource pack for blocks, items, or tools, it may include its own menu textures that overwrite the dark style from Black Keys Resource Pack. You can layer both packs so your world keeps its custom textures while your menus stay dark.
Setting the Correct Pack Order
1. From the start screen or pause menu, open Options and select Resource Packs.
2. Make sure both your world texture pack and Black Keys Resource Pack are placed in the right-hand Selected column.
3. Hover over Black Keys Resource Pack and click the up arrow until it sits at the very top of the Selected list.
4. Click Done so Minecraft reloads your active assets.
Confirming the Combined Setup
Minecraft loads resource packs from bottom to top, meaning the highest pack takes priority whenever two packs change the same screen. Putting Black Keys at the top ensures the game uses its solid black buttons, dark menu background, dark survival and creative inventories, and dark advancements screen, while still loading world blocks and tool sprites from the packs listed underneath it.