add button class

app.py

@@ -124,7 +124,7 @@ with gr.Blocks(css=css) as demo:
             # gr.Markdown(" ## Drop your image here")
             input_image = gr.Image(type="filepath")
         with gr.Column(elem_id="col-container"):
-            generate_button = gr.Button("Generate flat sketch", scale=0, variant="primary")
+            generate_button = gr.Button("Generate flat sketch", scale=0, variant="primary", elem_classes="btn btn-primary")
 
             result = gr.Image(label="Result", show_label=False)