Nobody knows how much a rainbow weighs, but it's...

It can go on your head. You can cut it. It can be deep pile or shag.

I make up worlds both big and small, with castles high where wonders call. No rules I keep, no lines I see, I am whatever you want me to be.

I’m aged but not alive, I can crumble or I can thrive. Mice may chase me in their dreams, Yet I’m not quite what I seem.

I sit in your hand and help you play, I move in all directions, left, right, or sway. Push me forward, pull me back with care, I control the action in a digitallair. What am I?