According to the present state of science, almost all universe (except for about 5%) is made 50-50 by dark matter and dark energy.
Things we really have no idea what they are!
In summary, scientists basically know nothing!
Honest scientists will admit that, but there is the minority of know everything pseudoscientists who are giving science a very bad name!
Dark matter was concocted to explain why galaxies hold together rather than just spinning apart into space. Dark energy was concocted to explain why the universe doesn’t collapse on itself, all to offset the supposed effect of all the dark matter. Or perhaps there is something wrong with the standard cosmological models.