/usr/share/themes/Xfce-saltlake/gtk-2.0/gtkrc is in gtk2-engines-xfce 3.2.0-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 | style "default"
{
    GtkButton::default_border         = {0, 0, 0, 0}
    GtkButton::default_outside_border = {0, 0, 0, 0}
    GtkButton::child_displacement_x   = 1
    GtkButton::child_displacement_y   = 1
    GtkButton::default_spacing        = 5
    GtkButton::focus-line-width       = 1
    GtkButton::focus-padding          = 0
    GtkCheckButton::indicator_size    = 15
    GtkRadioButton::indicator_size    = 15
    GtkMenuItem::selected_shadow_type = etched-in
    GtkPaned::handle_full_size        = 1
    GtkRange::slider_width            = 15
    GtkRange::stepper_size            = 15
    GtkRange::trough_border           = 0
    GtkScrollbar::min_slider_length   = 20
    GtkWidget::interior_focus         = 1
    xthickness = 2
    ythickness = 2
    fg[ACTIVE]        = "#000000"
    fg[INSENSITIVE]   = "#717170"
    fg[NORMAL]        = "#000000"
    fg[PRELIGHT]      = "#000000"
    fg[SELECTED]      = "#ffffff"
    bg[ACTIVE]        = "#cdcdc9"
    bg[INSENSITIVE]   = "#e4e4e0"
    bg[NORMAL]        = "#e4e4e0"
    bg[PRELIGHT]      = "#ccc9c5"
    bg[SELECTED]      = "#3f993f"
    base[ACTIVE]      = "#e5e5e5"
    base[INSENSITIVE] = "#e4e4e0"
    base[NORMAL]      = "#ffffff"
    base[PRELIGHT]    = "#ccc9c5"
    base[SELECTED]    = "#ccc9c5"
    text[ACTIVE]      = "#000000"
    text[INSENSITIVE] = "#000000"
    text[NORMAL]      = "#000000"
    text[PRELIGHT]    = "#000000"
    text[SELECTED]    = "#000000"
    engine "xfce"
    {
	smooth_edge = false
    }
}
widget_class "*"          style "default"
style "thin" = "default"
{
    xthickness = 1
    ythickness = 1
}
widget_class "*Progress"  style "thin" 
class "*Progress"         style "thin" 
widget_class "*MenuItem*" style "thin" 
class "*MenuItem*"        style "thin" 
# This is for ROX-Filer
# 
style "rox" = "default"
{
  bg[NORMAL] = "#ffffff"
  bg[ACTIVE] = "#ffffff"
}
widget_class "*Collection" style "rox"
# This is for the window borders (xfwm4 & metacity)
# 
style "titlebar" = "default"
{
    bg[SELECTED]      = "#3f993f"
    fg[SELECTED]      = "#ffffff"
    bg[INSENSITIVE]   = "#cdcdc9"
    fg[INSENSITIVE]   = "#000000"
}
widget "xfwm"	          style "titlebar"
class "MetaFrames"        style "titlebar"
widget_class "MetaFrames" style "titlebar"
 |