How to import CSS rules?

If I have two css files, in the same folder :

main.css where I have several rules, for example :

body {
    background-color: #000000;
    margin-top: 50px;
}

and the jxcore.css (where there is still nothing)

And two html files, which are:

main.html (respective for main.css) and jxcore.html (respective for jxcore .css)

How could import only the body rule from main.css to jxcore.html , without having to call it from the html file with <link> , since the file main.css , have other rules that I do not want , is it possible?