I have noticed that a lot of times when I load up a website or PWA, it will show up in white for a split micro second and then turn dark. I didn't have a problem with that, but I realized that this slows down my computer and (I think) makes the CPU work an extra step for my computer, making it less efficient.
I am being very stubborn about not enabling the light/dark UI system theme flag on my Chromebook because I don't want the elements to be black on top of a black webpage.
The reason i am thinking about this is that my Chromebook has always gotten ridiculously long battery life, but the past few weeks it has been getting such lousy battery life it's not even funny and has even started to slow down a little bit. I'm trying to do what I can to reverse that.