GTK+3.0 - Scrollbar on Treeview/ScrolledWindow - CSS properties to control scrollbar - gtk3

Question

Developing on GTK+3.0 (3.22.30), openbox on X11, Ubuntu 18.04 server.
I've have been struggling to figure out the CSS model to control the appearance of the scrollbar on a GtkTreeView ScrolledWindow. I have had very limited success. The only thing I have been able to control is the color of the slider when clicking/moving on it and the background color of the trough. The other properties don't seem to have any effect. I found that the color property of the trough is not supported and seems to cause a parsing error.
The application uses a touch screen so I need the scroll bar to appear all the time, not just when a cursor-pointer hovers over the control. There is no cursor-pointer in the touch application.
I have tried these CSS definitions below. Some of this is simply experimental trying to get something to work. I've tried moving the width, min-width and the 'has-xx-stepper' but they don't seem to have any effect. I'm still stuck with the same simple default slider but with some basic color control. I can't interpret how the CSS node model for a scrollbar is to be referenced as I can't find an example.
scrollbar {
has-backwards-stepper: true;
has-forward-stepper: true;
has-secondary-backward-stepper: true;
has-secondary-forward-stepper: true;
min-width: 80;
}
trough {
background-color: #00ee00;
}
slider {
color: #00FF00;
slider-width: 80;
min-width: 80;
has-backwards-stepper: true;
has-forward-stepper: true;
}
Using the GTK+ Inspector (which allows some examination of Gtk apps' CSS attributes) I can't find the 'has-backwards-stepper' and other properties as referenced in the GTK3 GtkScrollbar documentation. This is handy place to test the CSS syntax but I can't figure out how to control the appearance as I need.
What is the syntax that I should be using to get the stepper buttons, to fix the width and have it appear at all times? A pointer to the documentation that explains this would be helpful. I've already been through the GTK 3 CSS Overview exhaustively which is no help here.

Answer 1

I was able to determine that the has-xxxx-stepper properties appear to be read only but don't actually connect to anything as I can change.
I was able to get the scrollbar to appear to the right of the scrollwindow with the 'overlay-scrolling' property.
sw = gtk_scrolled_window_new(NULL, NULL);
gtk_container_set_border_width( GTK_CONTAINER(sw), 0 );
gtk_scrolled_window_set_policy( GTK_SCROLLED_WINDOW(sw), TK_POLICY_NEVER, GTK_POLICY_ALWAYS ); //scroll bars
//Set scrollbar to ALWAYS be displayed and not as temporary overlay
g_object_set( sw , "overlay-scrolling", FALSE , NULL);
I was able to further control the width of the scrollbar trough with this:
GtkWidget * ptrVscrollBar = gtk_scrolled_window_get_vscrollbar ( TK_SCROLLED_WINDOW(sw) );
g_object_set( ptrVscrollBar ,
"width-request", 30 ,
"margin-bottom", 30 ,
"margin-top", 30 ,
NULL);
Update: I found the that CSS syntax was a little different for the slider. With some experimentation I was able to override the width and height of the slider component. The px units are required for these property values and without them they are ignored.
slider {
min-width: 28px;
min-height: 80px;
}
I have not figured out how to enable the stepper buttons to appear. Do these now have to be manually / separately created with GTK3? I have some prototype code using the vadjustment object properties of the scroll window but what a pain to hook up for every scroll bar I have.