Update app.py

app.py

@@ -3937,7 +3937,10 @@ css = """
 }
 
 body {
-    background-color: #87CEEB;
+    background-image: url('your-image-url.jpg');
+    background-size: cover;
+    background-position: center;
+    background-repeat: no-repeat;
     color: #fff;
 }