Because you are using the mozilla format in chrome.
In chrome, below the code area is where you choose where it applies to.
https://forum.userstyles.org/discussion/53989/why-doesnt-my-gmail-script-work
Ah, indeed. Also, to convert a mozilla-format userstyle click the Import button in the Stylish editor.
Why doesn't my gmail script work?
I have this really ugly pink bar at the top of my gmail that I'm trying to change the color of.
I think this should work, but it doesn't: http://i.imgur.com/Je8QF7j.png
Any help would be appreciated.