When I open this image in Safari, this is what I see:
https://i.stack.imgur.com/KbyGP.png
However, this is the code I have:
https://i.stack.imgur.com/4wEf0.png
References:
How to Remove WebKit's Banana-Yellow Autofill Background
Remove forced yellow input background in Chrome - even though it mentions Chrome, it still relates to webkit-autofill
I attempted to use
background-color:white !important;
to override the locked CSS. The debug tool displayed the User Agent Stylesheet background-color as crossed out, but the color did not change and the custom style was in effect.
This situation left me puzzled; I am unsure why I am unable to modify the User Agent Stylesheet.