I would define kindness as being and doing positive things without expecting anything in return.
I think that this is a good definition of kindness because kindness can be many different things, but it will always be a positive act. I also think that just doing positive things but not having a positive attitude is not kindness. You can be doing a very kind act, but your attitude towards it could lower that act of kindness. I think it’s important to add the last part of the definition because if you are expecting something in return or doing it for, say, a reward of some kind, it is not an act of kindness. You wouldn’t be doing the task to be kind but what you will receive for doing the task.