Currently, no such option has been made available by Jisho.
Instead, you can use the Chrome Dark Theme extension. It decreased a good amount of my eye stress.
https://chrome.google.com/webstore/detail/go-dark-mode/jlkdofajddljankdeiafmcdahbddfpml?gclid=Cj0KCQjwv5uKBhD6ARIsAGv9a-zoET_TrPVaZEhhXLdDjcmn-mryH6iWha01tjmelj2TVoyfzkvq0f8aAqvfEALw_wcB
I would as well very much appreciate it. Please do it!!
I will add dark mode to Jisho at some point in the future, I'm just not sure when.
In the meantime there's browser extensions available, such as the one @Prushetty suggested. https://darkreader.org also looks like it works well with Jisho.
There's also user styles available: https://userstyles.org/styles/browse/jisho
Request for Dark Mode
Is it possible to make dark mode an option on this website? This would make the long hours I spend here easier on my eyes.