feat: adjust html preview size

app.py

@@ -513,12 +513,15 @@ def update_preview_from_html(html_content: str) -> str:
         safe_html_content = html_content.replace('"', """)
         preview_html = f"""
         <div style='padding: 20px; width:100%; height:520px; background: #fff; border: 1px solid #eee; border-radius: 8px; display: block;'>
-            <iframe srcdoc="{safe_html_content}"
-                width="100%" 
-                height="100%" 
-                style="border:none; border-radius:8px; overflow:hidden;"
-                sandbox="allow-scripts allow-same-origin">
-            </iframe>
+            <div style='display: block; align-items: center; margin-bottom: 10px;'>
+            </div>
+            <div id='animation-container' style='height: 100%; display: block; justify-content: center; align-items: center; background: #fafafa; border-radius: 4px; padding: 20px; box-sizing: border-box;'>
+                <iframe srcdoc="{safe_html_content}"
+                    width="100%" height="100%" 
+                    style="border:none; border-radius:8px; overflow:hidden;"
+                    sandbox="allow-scripts allow-same-origin">
+                </iframe>
+            </div>
         </div>
         """
         return preview_html