Now that things have calmed down, I'll share the dark CSS I've been working on. I'm still working on the light one with the Spring theme, but it's not ready yet. I'm going to use a trip for sharing these things so people don't get confused.
How to use this file:
1. You need Onee Chan here: https://github.com/nebukazar/OneeChan
(scroll down until you see "##Click to Install' and click it.
2. I also heavily recommend 4Chan X to be used alongside this. ( https://github.com/ccd0/4chan-x
3. Download this file here: https://files.catbox.moe/et2qad.json
(right click, save as)
4. In Onee Chan, go the Themes tab and hit that Import button on the bottom left. Select the file you just downloaded. It will now be at the bottom of the Themes list which you can then select for "red" and/or "blue" boards.
5. The font I'm using isn't there by default, you need to download it here: http://www.dafont.com/neuton.font
. Once installed, scroll down to the bottom of the main Onee Chan tab to Fonts and click the (load) text next to Font Family. It will load all the fonts on your system which might take a little while. Select Neuton and if applicable, change the size as well.
NOTE: In the picture there's a pink border around each post, but I disabled it. To get it back, remove the two "#" marks in front of the two lines in the "Custom CSS" text under the configuration window for the theme's colors. This may also require editing in the Onee Chan .js file but I can't remember.
You can also customize the theme's colors and such afterwards; there's nothing locked in place.