changes the theme of youtube into a Modified White to black gradient.
< Feedback on Black Youtube by Panos modified by Sonic0170
as far as i understand this style based script was only created to work with stylish and compatibility with greasemonkey is just an added plus even though panosbabo did not intend it, whether it will work with any other script manager is completely unknown and due to the dramatic differences between windows, mac OS X and linux, it is completely unknown to me if it would work properly or at all within any operating environments beyond the windows based version of firefox or using anything beyond greasemonkey or stylish.
In your case this script might not be compatible with either mac OS, tampermonkey, or both and since i did not write this script, I don't know how to make it work.
you can ask Panosbabo for help at https://userstyles.org/users/102969 but he may not wish to update for compatibility for anything beyond stylish.
Oh, I thought I could get the same things with Tampermonkey or greasymonkey, maybe that was wrong. Thanks for your reply.
Registered to say that the same behaviour noted by mantisin happens on my system.
Black Youtube by Panos modified by Sonic0170 Version 2016.09.06
Windows 10 x64
Chrome Version 54.0.2840.71 m
Tampermonkey v4.1.10.
Cannot install to tampermonkey by click "Install this script" button
Using chrome on macOS, when I click install button, chrome just download it as a .js file, and toast a message, "Apps, extensions, and user scripts cannot be added from this website." No reactions from Tampermonkey.
Then I tried another script, it just work well.