How do I set the background colour of the window when the page loads?

[Keithyumi]

I replaced the index.html file in the lib/front folder to implement a custom IDE, the background is white until the page is fully rendered, making the user feel as if the program is stuck, how do I change the background colour to diminish this experience.

[Keithyumi]

How can I control the timing of the browser window display?

[msujew]

@Keithyumi You might want to use a splash screen. See here.