How to customise the appearance of the menubar and scrollbar on Linux?

Question

I am using Mathematica 12 on linux and would really like the dracula type theme for mathematica to match the overall theme of my system. I can use stylesheet to modify the notebook theme but this does not change the Menubar and the Scrollbars. Is there a way to change the colorscheme of the Menubar and the Scrollbars? Thanks for your time.

Answer 1

Thanks to @ihojnicki, this is in fact possible.

Since the frontend looks in ~/.Mathematica/FrontEnd/frontend.css for custom Qt CSS, we can write our own to change the colours of the various elements.

Creating that file and adding the contents

QScrollBar:vertical {
  background: green;
  width: 20px;
}
QScrollBar::handle:vertical {
  background: red;
  min-height: 0px;
}
QMenu {
  background-color: #ababab; /* sets background of the menu */
  border: 1px solid black;
}

QMenu::item {
  /* sets background of menu item. set this to something non-transparent
        if you want menu color and menu item color to be different */
  background-color: transparent;
}

QMenu::item:selected {
  /* when user selects item using mouse or keyboard */
  background-color: #654321;
}

QMenuBar {
  background-color: qlineargradient(
    x1: 0,
    y1: 0,
    x2: 0,
    y2: 1,
    stop: 0 lightgray,
    stop: 1 red
  );
  spacing: 3px; /* spacing between menu bar items */
}

QMenuBar::item {
  padding: 1px 4px;
  background: transparent;
  border-radius: 4px;
}

QMenuBar::item:selected {
  /* when selected using mouse or keyboard */
  background: #a8a8a8;
}

QMenuBar::item:pressed {
  background: #888888;
}

we can get this frankly beautiful colour arrangement:

Reading some of the Qt documentation should get you much of the way to a matching Frontend.