Resource packs are excellent ways to spice up your Minecraft server or use on an adventure map without changing the game a ton. Resource packs can customize things such as models, textures, sounds and UI. When you install them on your server, all joining players will need to download them when prompted. These are the steps to install a resource pack onto your server.
1. Find a resource pack you like from a website such as CurseForge. In this guide, we'll be using Mandala's GUI - Dark mode
2. Once you have downloaded the pack, you'll see that it's in a zip format.
3. To install your resource pack, you'll need to host the pack. Go to mc-packs.net
4. Select Choose File and choose the zip file you downloaded earlier
5. Click Upload and then copy the Download URL
6. In the Control Panel, navigate to the Basic Server Settings
7. Paste the link under Set Resource Pack
8. Save and Restart the server, players should now need to use this pack to join the server.