Serving static files recursively with go

I'm using sveltekit as my frontend for an app I'm working on. I've chosen a static adapter in the svelte.config.js which outputs all necessary components as static files. Here is the structure of my static directory.

The upper most files load, however, files in static/_app do not

func main() {
    router := mux.NewRouter()
    router.Handle("/", http.FileServer(http.Dir("static")))
    router.HandleFunc("/large-files", largeFilesHandler).Methods("OPTIONS", "POST")
    router.HandleFunc("/delete-file", deleteFileHandler).Methods("DELETE", "OPTIONS")
    logrus.SetLevel(logrus.ErrorLevel)
    err := http.ListenAndServe(":8000", router)
    if err != nil {
        logrus.Fatal(err)
    }

}

And in my svelte.config.js

import adapter from '@sveltejs/adapter-static';
import preprocess from 'svelte-preprocess';

/** @type {import('@sveltejs/kit').Config} */
const config = {
    // Consult https://github.com/sveltejs/svelte-preprocess
    // for more information about preprocessors
    preprocess: preprocess(),
    kit: {
        adapter: adapter({
            pages: '../static',
            assets: '../static',
        })
        ,
        prerender: { default: true }
    }
};

export default config;

Update:

If I remove the html files, I get the directory list, but all of these options fail with a 404

mux handles static files differently.

    router.PathPrefix("/").Handler(http.FileServer(http.Dir("./static")))