diff --git a/install-mdbook.sh b/install-mdbook.sh
index 04e690d6a1ff..abd812585fc2 100755
--- a/install-mdbook.sh
+++ b/install-mdbook.sh
@@ -1,10 +1,10 @@
 #!/bin/bash
 # The --locked flag is important for reproducible builds. It also
 # avoids breakage due to skews between mdbook and mdbook-svgbob.
-cargo install mdbook --locked --version 0.4.37
+cargo install mdbook --locked --version 0.4.44
 cargo install mdbook-svgbob --locked --version 0.2.1
 cargo install mdbook-pandoc --locked --version 0.9.3
-cargo install mdbook-i18n-helpers --locked --version 0.3.3
+cargo install mdbook-i18n-helpers --locked --version 0.3.5
 cargo install i18n-report --locked --version 0.2.0
 # these packages are located in this repository
 cargo install --path mdbook-exerciser --locked
diff --git a/theme/book.js b/theme/book.js
index 38ca7068ab04..69a0fc67a337 100644
--- a/theme/book.js
+++ b/theme/book.js
@@ -290,7 +290,7 @@ function playground_text(playground, hidden = true) {
                 }
 
                 var clipButton = document.createElement('button');
-                clipButton.className = 'fa fa-copy clip-button';
+                clipButton.className = 'clip-button';
                 clipButton.title = 'Copy to clipboard';
                 clipButton.setAttribute('aria-label', clipButton.title);
                 clipButton.innerHTML = '<i class=\"tooltiptext\"></i>';
@@ -323,7 +323,7 @@ function playground_text(playground, hidden = true) {
 
         if (window.playground_copyable) {
             var copyCodeClipboardButton = document.createElement('button');
-            copyCodeClipboardButton.className = 'fa fa-copy clip-button';
+            copyCodeClipboardButton.className = 'clip-button';
             copyCodeClipboardButton.innerHTML = '<i class="tooltiptext"></i>';
             copyCodeClipboardButton.title = 'Copy to clipboard';
             copyCodeClipboardButton.setAttribute('aria-label', copyCodeClipboardButton.title);
@@ -354,6 +354,10 @@ function playground_text(playground, hidden = true) {
     var themeToggleButton = document.getElementById('theme-toggle');
     var themePopup = document.getElementById('theme-list');
     var themeColorMetaTag = document.querySelector('meta[name="theme-color"]');
+    var themeIds = [];
+    themePopup.querySelectorAll('button.theme').forEach(function (el) {
+        themeIds.push(el.id);
+    });
     var stylesheets = {
         ayuHighlight: document.querySelector("[href$='ayu-highlight.css']"),
         tomorrowNight: document.querySelector("[href$='tomorrow-night.css']"),
@@ -382,7 +386,7 @@ function playground_text(playground, hidden = true) {
     function get_theme() {
         var theme;
         try { theme = localStorage.getItem('mdbook-theme'); } catch (e) { }
-        if (theme === null || theme === undefined) {
+        if (theme === null || theme === undefined || !themeIds.includes(theme)) {
             return default_theme;
         } else {
             return theme;
@@ -510,6 +514,7 @@ function playground_text(playground, hidden = true) {
     var sidebar = document.getElementById("sidebar");
     var sidebarLinks = document.querySelectorAll('#sidebar a');
     var sidebarToggleButton = document.getElementById("sidebar-toggle");
+    var sidebarToggleAnchor = document.getElementById("sidebar-toggle-anchor");
     var sidebarResizeHandle = document.getElementById("sidebar-resize-handle");
     var firstContact = null;
 
@@ -524,17 +529,6 @@ function playground_text(playground, hidden = true) {
         try { localStorage.setItem('mdbook-sidebar', 'visible'); } catch (e) { }
     }
 
-
-    var sidebarAnchorToggles = document.querySelectorAll('#sidebar a.toggle');
-
-    function toggleSection(ev) {
-        ev.currentTarget.parentElement.classList.toggle('expanded');
-    }
-
-    Array.from(sidebarAnchorToggles).forEach(function (el) {
-        el.addEventListener('click', toggleSection);
-    });
-
     function hideSidebar() {
         body.classList.remove('sidebar-visible')
         body.classList.add('sidebar-hidden');
@@ -547,22 +541,16 @@ function playground_text(playground, hidden = true) {
     }
 
     // Toggle sidebar
-    sidebarToggleButton.addEventListener('click', function sidebarToggle() {
-        if (body.classList.contains("sidebar-hidden")) {
+    sidebarToggleAnchor.addEventListener('change', function sidebarToggle() {
+        if (sidebarToggleAnchor.checked) {
             var current_width = parseInt(
                 document.documentElement.style.getPropertyValue('--sidebar-width'), 10);
             if (current_width < 150) {
                 document.documentElement.style.setProperty('--sidebar-width', '150px');
             }
             showSidebar();
-        } else if (body.classList.contains("sidebar-visible")) {
-            hideSidebar();
         } else {
-            if (getComputedStyle(sidebar)['transform'] === 'none') {
-                hideSidebar();
-            } else {
-                showSidebar();
-            }
+            hideSidebar();
         }
     });
 
@@ -662,12 +650,12 @@ function playground_text(playground, hidden = true) {
 
     function hideTooltip(elem) {
         elem.firstChild.innerText = "";
-        elem.className = 'fa fa-copy clip-button';
+        elem.className = 'clip-button';
     }
 
     function showTooltip(elem, msg) {
         elem.firstChild.innerText = msg;
-        elem.className = 'fa fa-copy tooltipped';
+        elem.className = 'clip-button tooltipped';
     }
 
     var clipboardSnippets = new ClipboardJS('.clip-button', {
diff --git a/theme/index.hbs b/theme/index.hbs
index 625d6443be66..bbbdc3bdc3e0 100644
--- a/theme/index.hbs
+++ b/theme/index.hbs
@@ -1,5 +1,5 @@
 <!DOCTYPE HTML>
-<html lang="{{ language }}" class="{{ default_theme }}" dir="{{ text_direction }}">
+<html lang="{{ language }}" class="{{ default_theme }} sidebar-visible" dir="{{ text_direction }}">
     <head>
         <!-- Book generated using mdBook -->
         <meta charset="UTF-8">
@@ -52,15 +52,17 @@
         <!-- MathJax -->
         <script async src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
         {{/if}}
-    </head>
-    <body class="sidebar-visible no-js">
-    <div id="body-container">
+
         <!-- Provide site root to javascript -->
         <script>
             var path_to_root = "{{ path_to_root }}";
             var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "{{ preferred_dark_theme }}" : "{{ default_theme }}";
         </script>
-
+        <!-- Start loading toc.js asap -->
+        <script src="{{ path_to_root }}toc.js"></script>
+    </head>
+    <body>
+    <div id="body-container">
         <!-- Work around some values being stored in localStorage wrapped in quotes -->
         <script>
             try {
@@ -82,19 +84,16 @@
             var theme;
             try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
             if (theme === null || theme === undefined) { theme = default_theme; }
-            var html = document.querySelector('html');
+            const html = document.documentElement;
             html.classList.remove('{{ default_theme }}')
             html.classList.add(theme);
-            var body = document.querySelector('body');
-            body.classList.remove('no-js')
-            body.classList.add('js');
+            html.classList.add("js");
         </script>
 
         <input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
 
         <!-- Hide / unhide sidebar before it is displayed -->
         <script>
-            var body = document.querySelector('body');
             var sidebar = null;
             var sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
             if (document.body.clientWidth >= 1080) {
@@ -104,41 +103,21 @@
                 sidebar = 'hidden';
             }
             sidebar_toggle.checked = sidebar === 'visible';
-            body.classList.remove('sidebar-visible');
-            body.classList.add("sidebar-" + sidebar);
+            html.classList.remove('sidebar-visible');
+            html.classList.add("sidebar-" + sidebar);
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <div class="sidebar-scrollbox">
-                {{#toc}}{{/toc}}
-            </div>
+            <!-- populated by js -->
+            <mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox>
+            <noscript>
+                <iframe class="sidebar-iframe-outer" src="{{ path_to_root }}toc.html"></iframe>
+            </noscript>
             <div id="sidebar-resize-handle" class="sidebar-resize-handle">
                 <div class="sidebar-resize-indicator"></div>
             </div>
         </nav>
 
-        <!-- Track and set sidebar scroll position -->
-        <script>
-            var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
-            sidebarScrollbox.addEventListener('click', function(e) {
-                if (e.target.tagName === 'A') {
-                    sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
-                }
-            }, { passive: true });
-            var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
-            sessionStorage.removeItem('sidebar-scroll');
-            if (sidebarScrollTop) {
-                // preserve sidebar scroll position when navigating via links within sidebar
-                sidebarScrollbox.scrollTop = sidebarScrollTop;
-            } else {
-                // scroll sidebar to current active section when navigating via "next/previous chapter" buttons
-                var activeSection = document.querySelector('#sidebar .active');
-                if (activeSection) {
-                    activeSection.scrollIntoView({ block: 'center' });
-                }
-            }
-        </script>
-
         <div id="page-wrapper" class="page-wrapper">
 
             <div class="page">