Arduino sketch fading individual LEDs

I have been trying to get something working over the last couple of weeks and it’s driving me crazy.

It sounds simple in my head and I’ve seen similar sketches around however I have no idea what I’m doing not through lack of trying however.

Either way I have 6 LED Neopixels (ws2812b) which set to specific colours. I would then like these LED’s to fade a random amount (however never completely off) and return to full brightness individually and not all at once like I’m getting at the moment.

Basically I want each LED to have its own colour and completely random fade animation on repeat.
Random duration of the fade animation as well as random fade amount for each LED.

That’s as best as I can explain what I need.

Hope you can help.

Many thanks
Tony