I have been trying to create a basic custom state card using the custom ui. I have looked at all of the examples I could find such as Fan Control, the Custom UI elements by andrey, etc. I copied the html files into www/custom_ui and added the yaml in customize.yaml. I tried enabling development mode but that caused other issues even loading the ui. I am running Home Assistant on a Raspberry Pi. I have tried to override the UI for a Fan, Switch, and custom component. I am able to get a custom component to work by creating a python file in custom_components.
Do I need to set up the development environment as show here to create a custom state card? I was just trying to place my files in www/custom_ui.
https://home-assistant.io/developers/development_environment/
Did you also edit the customize section of your config to indicate what device should use the custom ui?