Find stylesheets in all HTML Imports, as they are now deprecated https://github.com/TakayoshiKochi/deprecate-style-in-html-imports

findStylesheetsInAllHTMLImports-bookmarklet.html

<a href="javascript:(function(){var%20screl=document.createElement('script');screl.setAttribute('type','text/javascript');screl.setAttribute('src','https://gist.githubusercontent.com/tomalec/47f0acd910a729d0b6a2e55061e5c26e/raw/4843f8a32d971f0465871a2d26cf6cc5c88e1229/findStylesheetsInAllHTMLImports.js');document.body.appendChild(screl);})();">Find HTML Imported styles bookmarklet</a>

findStylesheetsInAllHTMLImports.js

function findStylesheetsInImportedDocs(doc, map) {
    map = map || {};
    // map = map || new Map();
    Array.prototype.forEach.call(doc.querySelectorAll('link[rel=import]'), (e) => {
        const importedDoc = e.import;
        if (importedDoc && !map[importedDoc]) {
            const styles = importedDoc.querySelectorAll('style,link[rel=stylesheet]');
            if (styles.length) {
                map[importedDoc.URL] = {
                    doc: importedDoc,
                    styles: styles
                };
                // map.set(importedDoc, styles);
            }
            findStylesheetsInImportedDocs(importedDoc, map)
        }
    });
    return map;
}
console.log(findStylesheetsInImportedDocs(document));