Update css and js for CDN

Author: oscarlevin via GitHub Actions

dist/_static/pretext/css/theme-boulder.css

@@ -155,7 +155,8 @@ window.addEventListener("DOMContentLoaded", function(event) {
             expander.classList.add('toc-expander');
             expander.classList.add('toc-chevron-surround');
             expander.title = 'toc-expander';
-            expander.innerHTML = '<span class="icon material-symbols-outlined" aria-hidden="true">chevron_left</span>';
+            // content of span is set by CSS :before rule.
+            expander.innerHTML = '<span class="icon material-symbols-outlined" aria-hidden="true"></span>';
             tocItem.querySelector(".toc-title-box").append(expander);
             expander.addEventListener('click', () => {
                 toggleTOCItem(expander);