Does anyone know of/have any CustomCSS that they could share, that has a dark background? All of this white just hurts my eyes too much, but the free ones I find have the default white. ;A;

This is something someone shared in the help section this past week. Of course you can change the colours to whatever suits you and/or your current layout. :) I hope this helps.

{background-color:}

.ui.segment {background-color: ;}

Here. They have a galactic one, which is dark, and there are two editable ones that you can change different parts to suit your liking. I'm using that right now. n.n