Bright white page before loading anything

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Every time a link opens in a new tab and I go there automatically, the page is white before the website loads. Is there a way to change this to default something dark? This is giving me bad eye strain and this was unfortunately the big reason for me to switch from Chrome to Firefox. Even though I loved Chrome, my eyes are more important. Vivaldi seems a lot more promising and I wondered if there was a way to modify that white page, like I've been able to do as well in Firefox. I've tried googling around for the css solution of its commons.css but nothing gave me the solution. Maybe there's other tricks required? So far only that white page before anything gets loaded is what's keeping me from trying Vivaldi. I'd probably suggest to make that default unloaded page listen to the chosen background color for your speed dial page for ease of use. I've set the speed dial one to something dark already, so it'd only make sense. (The white page before loading also happens when you're in a speed dial page. Once a site really has loaded, this problem doesn't occur anymore for that tab)

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I think the following falls into the same category:

If you're viewing an image in Vivaldi, the surrounding area is bright white as well. It'd be nice if it'd also adjust to the dark theme that I've chosen for this browser.

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Oh , this is annoying, and also same category still:

If you've watched a youtube video in fullscreen, apparently the browser resolution changes. So when you get back to the browser gui, the website you visited is like 1/4th of your browser screen, the rest of the area is bright white. Then the site resizes back to the full browser window as it was originally. So when I revisit my other tabs after having watched a video in fullscreen, they all have this and I will have to constantly look at something bright white while those pages realign themselves back to where they should be.

It'd be less of an issue if the 'empty' area simply was configurable to be something dark. Now my eyes are having a hard time and I'm afraid to watch any videos in fullscreen now.