I read that the dark matter formed a halo, and dust and gas inside that halo formed the first ever galaxies.I am curious to know whether the dust and gas formed the galaxy inside a previously formed halo or whether the halo formed around the dust and gas.

I am an amateur

I read that in the early Universe dark matter forms halos, and dust and gas inside those halos formed the first ever galaxies. I am curious to know whether the dust and gas formed the galaxy inside a previously formed halo, or whether the halo formed around the dust and gas.