About:
This applies a dark reddish theme to every page on jisho.org that I could find. If I missed some element or you found another bug (or have a suggestion) please contact me with it and I'll see what I can do.

Made by me (wekateka) using Stylish, tested in the latest stable Firefox.

Update history:
26-06-2015: Styled some focused input elements that I missed.
06-12-2015: Styled some more missed elements; Fixed text on Wanikani info overflowing.
21-03-2016: Fixed some buttons having a white background on hover; Made the rectangle containing the "More" link in radical/handwriting view a nicer size. Added support for Jisho classic, and the classic forum.
25-03-2016: Used modified fix from Jisho.org forum user JBRadio to make the custom logo scale on smaller screens.
03-04-2016: Applied more suggestions from forum user JBRadio; Gave the Links span in the search results a hitbox that does not actually stretch over the whole page horizontally.

Other things:

For chrome users, JBRadio is creating a nice extension for jisho.org that includes this theme (modified for chrome). https://github.com/JBRadio/Chrome-Extension-for-Jisho.org