style: add modern-scrollbar class to improve scrollbar appearance

Introduce the modern-scrollbar class to enhance the visual consistency of scrollbars across the application. This class provides a cleaner and more modern look for scrollbars in WebKit and Firefox browsers.

app/components/workbench/EditorPanel.tsx

@@ -114,7 +114,7 @@ export const EditorPanel = memo(
                   </div>
                 )}
               </PanelHeader>
-              <div className="h-full flex-1 overflow-hidden">
+              <div className="h-full flex-1 overflow-hidden modern-scrollbar">
                 <CodeMirrorEditor
                   theme={theme}
                   editable={!isStreaming && editorDocument !== undefined}