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Goodreads fixed search & navbar

Can someone help me create a script that can make Goodreads' search and navigation bar become fixed (follows us when we scroll down)
It's this part that I'm talking about:

Thank you in advance.

I would do it with Stylish addon:

@-moz-document domain("goodreads.com") {
#siteheader {
    position: fixed;
    z-index: 99;
}
.mainContentFloat {
    margin-top: 64px;
}
}

Thanks but it's slightly askew (too much to the left) and overlaps the main body site.
Here's the screenshot:

I'm not logged in so everything's fine, see the screenshot. Anyway you don't need a script, a userstyle is sufficient and https://forum.userstyles.org/ seems a better place to ask in my opinion.