WkWebView background always white

I have something that bugs me out for a long time now and I cannot fix it by myself. Before loading an HTML into a WkWebView, the background is always white. I tried dark mode but that didn’t help. Anyone knows a code that can fix this (or API that I am missing)?

hey there!
check the code in this link
https://www.w3schools.com/tags/att_body_bgcolor.asp