Update app.py

app.py

@@ -70,7 +70,8 @@ def upload_sketch(file):
 scripts = """
 async () => {
     console.log('Loaded...');
-    
+    parent.document.body.style.backgroundColor = "black";
+
     globalThis.theSketchDownloadFunction = () => {
         console.log("test")
         var link = document.createElement("a");