Add comprehensive white background targeting html, body, and .gradio-app

Target multiple elements to ensure complete white background coverage on HuggingFace Spaces.
This should eliminate any remaining black/dark margins or background areas.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

app.py

@@ -139,6 +139,10 @@ with gr.Blocks(
     theme=gr.themes.Default(),
     title="MobileNetV2 Classification",
     css="""
+    html, body, .gradio-app {
+        background: white !important;
+        background-color: white !important;
+    }
     .gradio-container {
         max-width: 1200px !important;
         margin: auto !important;