Maybe some of that code will work for D2 ... try it and see. If not ... see lesson 1 and 2 above.
.header .tbtn, .top-header {
background: #ffffff!important;
}
Gave this a try for whole code you gave, only this one was working. .
I have tried your method too before this, using inspection method a week ago, the inspect element theme gave me .adapupdate as the place to change the color, when I did, it looked okay in webview and mobile.. but looks broken in tablet view. That's why came here for a solution.
And the inspect method doesnt change all the text colors in the bar, I have to choose each text circled below (which tells me it's not right way to do).