fix theme picker again

docs/assets/plugins/theme-picker/theme-picker.css

@@ -2,6 +2,7 @@
   position: fixed;
   top: 1rem;
   right: 1rem;
+  z-index: 30;
 }
 
 .theme-picker:not(:defined) {

docs/assets/plugins/theme-picker/theme-picker.js

@@ -53,7 +53,7 @@
           <sl-menu-item value="auto">Auto</sl-menu-item>
         </sl-menu>
       `;
-      document.querySelector('.content').prepend(dropdown);
+      document.querySelector('.sidebar-toggle').insertAdjacentElement('afterend', dropdown);
 
       // Listen for selections
       const menu = dropdown.querySelector('sl-menu');