You see me right now
If you look up from tech and
Gasp at my beauty
I am everything
From the tiny to the big
I'm almost empty
What am I?
Looking up could be a reference to the stars in that portion of space. From a certain view things can be/look small or big and take a volume of space. I'm almost empty, can refer to all the areas that have no space in comparison to that which takes space.
I had a moment of inspiration and thought of an another possible answer:
If you look up you realize everything has a shadow even the phone you may be looking at. It can be tiny or large, it comes from everything, and it is basically empty.
It could be beautiful, but this is the possible exception to this answer.
"Space" (meaning Outer Space as indicated by the asker) is a bad answer. You see me right now: I do not see Outer Space right now. If you look up from tech: I still do not see Outer Space. I am everything: Outer Space is not everything, it is not Earth or people for example.
Atoms fit every line. And yes they are mostly empty.