Atheism is all about taking a positive position that there are no supernatural beings: that's pretty much it.
I quibble on two counts: firstly, while most atheists would agree there are no supernatural beings, one can be atheist whilst holding there are supernatural beings just no Gods. Secondly, I
don't hold the positive belief that there are no supernatural beings, that follows from the belief that you can determine how the world actually is by investigation and the fact that we find no trace of supernatural beings.