Theme widget category for dragging files into containing folders

[scott092707]

[Also asked at the GitHub Mate/Caja discussion site, but no answer yet.]

I just installed a gtk theme (“Ambiance-RW”) and then modified it so that the scrollbars are more visible on my 49" UHD TV-as-monitor.
However, the theme does not have what the previous one had: when I select files in Caja and drag them into a button on the location bar,
the folder-button’s border became green, so that I knew it hit it right. Now, it does not change at all…
I don’t know themes much at all, and have no idea what type of widget (in gtk-widgets.css, I assume…) I should look for, and what properties.
Dragging folders into the button is not quite “hovering”, and not quite “selected”, …

Could anyone tell me what I should be looking for?

I guess, since the button doesn’t change when I drag stuff into it (this still works - it just does not indicate it),
it is possible that that option is not in the file at all, and will have to be added…

Help, anyone … ?
…
I have now found “Pathbar”, which may be the category I need, but after finding something elsewhere regarding “dragging”, and copying/modifiying it as shown below, it DOES change, but only when dragging a path tab button (which cannot be done with “breadcrumb” buttons anyway). I don’t want a change when the path tab or breadcrumb button itself is dragged, but when something is attempting to drag into the path tab (or breadcrumb) button.
I hope this description is clear enough, as (it is clear) I don’t know what I am doing.

.path-bar button:hover:backdrop,
.path-bar button.dragging:backdrop,
path-bar button:hover:backdrop,
path-bar button.dragging:backdrop {
    border-color: @fg_color;

This is the only gtk theme I have downloaded - the only theme already here was Raleigh, and “Default” and all I get from looking at files there, is:

#
# This theme is the default theme if no other theme is selected.
#

and

/*
 * Default keybinding set. Empty because it is implemented inline in the code.
 */

[gwillems]

Hi,

What you’re looking for is the :drop(active) pseudo-class.

You have to find the widget used a drop target (pathbar in the example below, to be rechecked) and apply the drop style on it.

pathbar:drop(active) {
	box-shadow: inset 0 0 0 1px forestgreen;
}

[scott092707]

Apparently, where I want the highlighting isn’t ‘path[-]bar’, for no change to that had any effect.
Caja’s forum suggested installing mate-themes and copying in what I needed.
‘Yaru*’ had the highlighting (the only themes that did, and were gtk-3.x), and I then grep’d ‘:drop(active)’, and copied in all lines that referenced a particular color.
I changed the green color to something a bit more noticeable, and added ‘border: 2px solid #xxxxxx’ to double the size of the highlighting.
[None of the lines referenced ‘path-bar’, so either I am misunderstanding what a path-bar is, or it is a sub-category of one of the things changed, such that changing that also changes path-bar…]

Thank you so much for the : ‘:drop(active)’ suggestion; it was key to the solution!