How to identify a Stack Exchange website before page load inside content script?

I'm writing a personal Chrome extension that modifies various things (i.e. styles) on various websites. That includes Stack Exchange. My extension is enabled on all websites so I have to differentiate between them based on window.location.

Currently I'm doing it like this:

// code executed before load
const host = window.location.hostname;
function hostIncludesAny(...strList) {
    for (const str of strList) {
        if (host.includes(str)) {
            return true;
        }
    }
    return false;
}
// ...
// more ifs here
// ...
if (hostIncludesAny("stackoverflow.com", "stackexchange.com", "serverfault.com", "superuser.com", "askubuntu.com")) {
    // apply styles for Stack Exchange network
}

I do it like this because stackexchange.com is a suffix for many subdomains and it gets them all. But some communities have their own domain like superuser.com or askubuntu.com and I have to include them manually.

Is there some information source (maybe response headers?) that connects all those websites?

I have already set up a background script, so I can message it to do something using available Chrome APIs, if that can help.

I don't think there's anything simple you can do to automatically detect these domains. There are only a handful of domains, it's easier to just list them explicitly.

Here's the list from a Tampermonkey script I've installed.

// @match       *://*.stackexchange.com/*
// @match       *://*.stackoverflow.com/*
// @match       *://*.superuser.com/*
// @match       *://*.serverfault.com/*
// @match       *://*.askubuntu.com/*
// @match       *://*.stackapps.com/*
// @match       *://*.mathoverflow.net/*
// @exclude     *://api.stackexchange.com/*
// @exclude     *://blog.*.com/*
// @exclude     *://chat.*.com/*
// @exclude     *://data.stackexchange.com/*
// @exclude     *://elections.stackexchange.com/*
// @exclude     *://openid.stackexchange.com/*
// @exclude     *://stackexchange.com/*