changed background color

app.py

@@ -120,7 +120,7 @@ def select_tile_weighting_method(tile_weighting_method):
 
 css = """
 body {
-    background: linear-gradient(135deg, #667eea, #764ba2);
+    background: linear-gradient(135deg, #F0F0F0, #FFFFFF);
     font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
     color: #333;
     margin: 0;