WordPress floating Update User button in dashboard?

I’ve tried to customize the CSS of WordPress so that I have a floating “Update User” button in the dashboard’s update profile page. I know which code to add:

{
    position: fixed;
    z-index: 1;
    top: 300px;
    right: 25px;
}

My problem is that even if I put it in a custom css file, or in the forms.css WordPress file, it doesn’t work.

I tried to assign it to a plentiful combination of ID and Classes (ex.: #profile-page.submit, #profile-page.button,…), but nothing worked. Any clue?

Thanks!