use alert class

apps/app/src/client/components/Common/RendererErrorMessage.tsx

@@ -2,14 +2,7 @@ import React from 'react';
 
 export const RendererErrorMessage: React.FC = () => {
   return (
-    <p
-      style={{
-        color: 'red',
-        backgroundColor: 'white',
-        padding: '0.75rem',
-        borderRadius: '4px',
-      }}
-    >
+    <p className="alert alert-warning">
       ⚠️ <strong>Developer Warning:</strong>{' '}
       Required renderer configuration is missing. Ensure <code>useRendererConfig()</code> is properly called in the component.
     </p>

apps/app/src/client/components/PagePresentationModal.tsx

@@ -88,7 +88,7 @@ const PagePresentationModal = (): JSX.Element => {
         <button className="btn-close" type="button" aria-label="Close" onClick={closeHandler}></button>
       </div>
       <ModalBody className="modal-body d-flex justify-content-center align-items-center">
-        { isLoading === false && rendererOptions == null && <RendererErrorMessage />}
+        { !isLoading && rendererOptions == null && <RendererErrorMessage />}
         { rendererOptions != null && isEnabledMarp != null && (
           <Presentation
             options={{