Just formatted a lot more stuff.
In Chrome / Firefox / Safari / IE (first few steps):
Copy the text on https://www.warlight.net/wiki/User:DanWL60/WL_Dark_Theme
Paste the text to Notepad (or another type of plain text editor e.g. Adobe Dreamworks).
Save the file as something.css - it has to be a .css file extention, file name doesn't matter.
Chrome / Firefox:
Remove the current stylesheet.
Select an addon that isn't User Styles. (Important!)
Reselect User Styles.
Open the stylesheet in a browser - copy it's web adress.
Select Install from URLs.
Paste the web address.
Name the stylesheet.
Menu -> Tools -> Internet Options -> Accessability -> Browse to where you saved the stylesheet -> Press OK -> Press OK.
Safari: similar to IE.
Edited 11/23/2016 23:39:50