Is it possible to override user stylesheet with !impotant via *.user.js?

Question

css

I apologize in advance, but alas, I am not strong in terminology, I try to comprehend as necessary.
For the google chrome browser, there is a certain extension (I don’t mention the name to avoid advertising), which creates its own class='test' for the body tag and assigns the following style to this class:
user stylesheet.test{margin-top:10px; !impotant}
Actually, I'm trying to assign a value of 0px to it through my *.user.js, but it doesn't work. If I understand correctly from Google, a user stylesheet with !impotant seems to have the highest priority.
Is there any way to assign 0px;?
PS My attempts: tried like this, top: -10px;

Answer 1

Example on jquery - jsfiddle.net/reuhkpwx Added
a pause for clarity.
In js, if you want, rewrite it yourself.

Answer 2

body.test{display: inline}
;-]

Answer 3

One question: why do you need such an extension? ..