Always visible brightness slider in integration. Backend-frontend relation

Hi, I am newbie here so apologies for all the faults in my question.
I am creating/updating some integration, and as I understand,
we extend abstract device class to match what integration device is supporting.
And basing on that setup(filled class attribute fields), frontend is created?(that’s how I percieve it currently)
As everything from backend works fine for me and I am able to make integrations, my issue is that in my integration there is always brightness slider(even if I set brightness property to return None) I don’t know, what is reference behaviour, or how front is being build. I believe I miss something. Is there documentation that shows how from base class HA is building frontend?
Let’s take for example Light Entity. Frontend adjusts while we change _attr_color_mode. Below example is rgbww mode. At the top, there is redundant brightness(or maybe I don’t understand concept of rgbww mode)

And that’s how entity looks.

  - NONE
  - FADE
  - RGB
  - BELL
  - rgbww
color_mode: rgbww
  - 7.368
  - 81.429
  - 140
  - 40
  - 26
  - 140
  - 0
  - 0
  - 92
  - 84
  - 0.64
  - 0.318
effect: NONE
friendly_name: TEST
supported_features: 4

So why is brightness accessible and where is documentation describing backend-frontend relation? :slight_smile: