Simplified theme management

• Settings / Head Content / Befort Content / HTML / Code
  <script>
     let theme = localStorage.getItem('theme');
     if (theme) {document.documentElement.setAttribute('data-bs-theme', theme);}
  </script>
• Settings Desin / Bootstrap
  Don't use auto mode to prevent the BSS from inserting its JS code.
• <nav class="navbar navbar-expand-md bg-primary" data-bs-theme="dark">
  Drop-down lists are dark because of the navbar
• Source code converted to HTML for correct indentation