I need some style changes to Kmail

I just started using Kmail again after about 10 years with Thunderbird and I found this lovely snippet when looking for a way to get rid of the ugly vertical HTML status area.

~ cat .local/share/hidehtmlstatusbar.qss
MessageViewer--HtmlStatusBar {
    max-width: 0px;
}

I’ve tweaked most of what I need within the gui settings but I still need a couple of things to be on par with my Thunderbird tweaks. Using the above .qss file, how can I…

  • reduce the fontsize in the folderlist pane
  • reduce the size of the folder icons in the folderlist pane
  • reduce the fontsize in the message pane header
  • change the background color of the message pane to white (regardless of theme color)