style: Improve markdown editor styling and functionality

- Update dark mode button icon and styling
- Add styling for new collection button
- Apply default iframe styles in preview pane
- Adjust vertical divider height in header buttons
- Improve handling of JSX-like attributes in markdown
- Add support for new collection functionality
- Refine file loading logic in view mode
- Improve dark mode toggle icon and integration
- Update UI for edit/view mode toggle button

static/app-tree.js

@@ -24,7 +24,7 @@
     function enableDarkMode() {
         isDarkMode = true;
         document.body.classList.add('dark-mode');
-        document.getElementById('darkModeIcon').textContent = '☀️';
+        document.getElementById('darkModeIcon').innerHTML = '<i class="bi bi-sun-fill"></i>';
         localStorage.setItem('darkMode', 'true');
 
         mermaid.initialize({
@@ -41,7 +41,7 @@
     function disableDarkMode() {
         isDarkMode = false;
         document.body.classList.remove('dark-mode');
-        document.getElementById('darkModeIcon').textContent = '🌙';
+        // document.getElementById('darkModeIcon').textContent = '🌙';
         localStorage.setItem('darkMode', 'false');
 
         mermaid.initialize({