GtkWidget focus line color

[James Robertson <j mesrobertson com>]

I am creating a GTK3 theme and want to have all indicator focus lines
a particular color in all states.

At the moment the focus lines uses the color of the widget state it is
on... for example:

.button {
    -GtkWidget-focus-padding: 2;
    -GtkWidget-focus-line-pattern: "\0\0";
    padding: 1px;
    border-width: 1px;
    border-style: solid;
    border-color: @theme_base_color;
    border-bottom-color: @gradient_from_color;
    background-image: -gtk-gradient(linear, left top, left bottom,
    from (@gradient_from_color),
    to (@gradient_to_color));
    color: @theme_fg_color;
}

.button:hover {
    border-color: @insensitive_color;
    background-image: none;
    background-color: @theme_selected_bg_color;
    color: @theme_selected_fg_color;
}

When the mouse hovers over a button the focus line color changes from
@theme_fg_color; to @theme_selected_fg_color but I might want it to
stay @theme_fg_color (or perhaps another color set globally).

In GTK2 I achieved this using the pixmap engine and an png image:

image
{
    function        = FOCUS
    recolorable     = TRUE
    file            = "Others/focus.png"
    border          = { 1, 1, 1, 1 }
    stretch         = TRUE
}

I am not using any GTK3 engine and had hoped something like this would
have worked (it doesn't).

*:focus {
    color: @theme_fg_color;
}

I am looking for something like an option
"-GtkWidget-focus-line-color" which doesn't exist or someone who knows
how I might achieve this.  I don't mind if I have to use an image and
have actually been trying to use border-images and such but haven't
been successful.

Thanks

James