CSS I'm new here.

[KittenKatja]

Hello Code Forum,

I found this forum for pressing questions, but I wanted to know a bit more about the forum before I ask them. (also googled it as bluntly as possible)
I have tried to upload 2 pictures as my pfp, both times it failed, I have uMatrix off already before registering, so I don't know where the problem lies.
Since I can't change my K, I'd like to change its colors instead, how do I do this without changing the pfp?

Now to the pressing questions.
For maybe 2 weeks now I am self-learning CSS through Stylus and W3Schools, but am far from being a CSS Ninja.
In youtube, there're 2 things whose colors I can't change, one being the empty search field background word and the second being the top-left three lines SVG.
In the youtube player, there are the buttons separated into left and right, I want to recolor the right ones into pink since I already have done so for the left.

I also have been looking into browser extensions; new page and frame colors specifically.
I used assets from an existing chrome extension, so I won't upload anything, there are just very confusing things I'd like to fix.
https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/themes/browser_theme_pack.cc shows me what I can change, I used a generator to do the grounding work first.
Anyone know a way [1] to fix this? Besides fixing the black background, I'd also like to color the dark gray area as well.
Also, I'd like to change the [2] gray text to something like pink with 0.5 opacity or grayish pink.

Also, it seems like the preview button in the editor is broken?