About the background color

[tri3ni]

Nice to meet you. I have created an application to annotation with this program.
In the demo, the background is black, is there any way to do this? In the meantime, I have created a .streamlit folder and specified the background as black in the files in it. However, only the area of this program is white (images and buttons).
I would like to know if you know the cause of this problem. Thank you in advance.