This snippet allows webpack-dev-server to hot reload stylesheets extracted with the ExtractTextWebpackPlugin

hot-reload-extracted-stylesheets

if (module.hot) {
    const hotEmitter = require("webpack/hot/emitter");
    const DEAD_CSS_TIMEOUT = 2000;

    hotEmitter.on("webpackHotUpdate", function(currentHash) {
        document.querySelectorAll("link[href][rel=stylesheet]").forEach((link) => {
            const nextStyleHref = link.href.replace(/(\?\d+)?$/, `?${Date.now()}`);
            const newLink = link.cloneNode();
            newLink.href = nextStyleHref;

            link.parentNode.appendChild(newLink);
            setTimeout(() => {
                link.parentNode.removeChild(link);
            }, DEAD_CSS_TIMEOUT);
        });
    })
}

In https://github.com/sheerun/extracted-loader I've employed an extra technique of removing old stylesheets with onload callback. It is more responsive and causes less issues. Also you need to remember to not reload 3rd party stylesheets.