Update app.py

app.py

@@ -309,13 +309,15 @@ def server(input, output, session):
     @render.ui
     @reactive.event(input.generate_plot)   
     def plot_ui():
-        brush_opts_kwargs = {}
-        brush_opts_kwargs["direction"] = 'xy'
-        brush_opts_kwargs["delay"] = 60  # Optional: adds a small delay for better performance
-        brush_opts_kwargs["delay_type"] = "throttle"
-        brush_opts_kwargs["clip"] = True
-        
-        
+        brush_opts_kwargs = {
+            "direction": 'xy',
+            "delay": 60,
+            "delay_type": "throttle",
+            "clip": True,  # This helps constrain the brush to the plot area
+            "fill": "#00000033",  # Optional: sets a semi-transparent fill
+            "stroke": "#000000"   # Optional: sets the brush border color
+        }
+            
     
         return ui.output_plot('plot', 
                             width='800px',