/usr/share/ldm/themes/joy/greeter-gtkrc is in ldm-themes 15.01.2.
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 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 | gtk_color_scheme = "fg_color:#ffffff\nbg_color:#424242\nbase_color:#FFF\ntext_color:#000000\nselected_bg_color:#c8c8c9\nselected_fg_color:#1A1A1A\ntooltip_bg_color:#F5F5B5\ntooltip_fg_color:#000"
style "default"
{
        fg[NORMAL]              = @fg_color
        fg[ACTIVE]              = @fg_color
        fg[INSENSITIVE]         = mix (0.4, @fg_color, shade (0.85, @bg_color)) #shaded to bg[INSENSITIVE]
        fg[PRELIGHT]            = @fg_color
        fg[SELECTED]            = @selected_fg_color
        
        bg[ACTIVE]              = shade (0.9, @bg_color)
	bg[NORMAL]              = @bg_color
        bg[INSENSITIVE]         = shade (0.95, @bg_color)
        bg[PRELIGHT]            = shade (1.03, @bg_color)
        bg[SELECTED]            = @selected_bg_color
        base[NORMAL]            = @base_color
        base[ACTIVE]            = shade (0.9, @selected_bg_color)
        base[INSENSITIVE]       = shade (0.95, @base_color)
        base[PRELIGHT]          = @bg_color
	base[SELECTED]          = @selected_bg_color
        
        text[NORMAL]            = @text_color
        text[ACTIVE]            = @text_color
        text[PRELIGHT]          = @text_color
        text[SELECTED]          = @selected_fg_color
        text[INSENSITIVE]       = mix (0.5, @text_color, @base_color)
	
	GtkRange::trough_border = 0
	GtkRange::slider_width = 15
	GtkRange::stepper_size = 15
	GtkEntry::progress-border = { 0, 0, 0, 0 }
	GtkScrollbar::min_slider_length = 15
	GtkCheckButton::indicator_size=10
	GtkCheckMenuItem::indicator_size=10
	GtkRadioButton::indicator_size=12
	GtkNotebook::tab_vborder = 1
	GtkNotebook::tab_hborder = 1
	xthickness = 1
	ythickness = 1
	NautilusIconContainer::dark_info_color="#888888"
	NautilusIconContainer::light_info_color="#bbbbbb"
	NautilusIconContainer::highlight_alpha=200
	GtkMenu::horizontal_padding=0
	GtkMenu::vertical_padding=0
	engine "mist"
 	{
	}
}
style "menuitem"
{
	ythickness = 2
	xthickness = 2
        fg[PRELIGHT]          = @selected_fg_color
}
style "menu" 
{
	ythickness = 2
	xthickness = 2
} 
style "entry"
{
	bg[SELECTED] = mix(0.35, @selected_bg_color, @base_color)
	fg[SELECTED] = @text_color
}
class "GtkWidget" style "default"
class "GtkMenu" style "menu"
class "GtkEntry" style "entry"
widget_class "*<GtkMenuItem>*" style "menuitem"
# Work around for http://bugzilla.gnome.org/show_bug.cgi?id=382646
# Note that the work around assumes that the combobox is _not_ in
# appears-as-list mode.
# This style does not affect GtkComboBoxEntry, it does have an effect
# on comboboxes in appears-as-list mode though.
style "mist-text-is-fg-color-workaround"
{
        text[NORMAL]              = @fg_color
        text[ACTIVE]              = @fg_color
        text[INSENSITIVE]         = mix (0.4, @fg_color, shade (0.85, @bg_color)) #shaded to bg[INSENSITIVE]
        text[PRELIGHT]            = @fg_color
        text[SELECTED]            = @selected_fg_color
}
widget_class "*.<GtkComboBox>.<GtkCellView>"   style "mist-text-is-fg-color-workaround"
style "mist-menuitem-text-is-fg-color-workaround"
{
        text[NORMAL]              = @fg_color
        text[ACTIVE]              = @fg_color
        text[INSENSITIVE]         = mix (0.4, @fg_color, shade (0.85, @bg_color)) #shaded to bg[INSENSITIVE]
        text[PRELIGHT]            = @selected_fg_color
        text[SELECTED]            = @selected_fg_color
}
widget "*.gtk-combobox-popup-menu.*"   style "mist-menuitem-text-is-fg-color-workaround"
# Work around the usage of GtkLabel inside GtkListItems to display text.
# This breaks because the label is shown on a background that is based on the
# base color set.
style "mist-fg-is-text-color-workaround"
{
        fg[NORMAL]            = @text_color
        fg[ACTIVE]            = @text_color
        fg[PRELIGHT]          = @text_color
        fg[SELECTED]          = @selected_fg_color
        fg[INSENSITIVE]       = mix (0.5, @text_color, @base_color)
}
widget_class "*<GtkListItem>*" style "mist-fg-is-text-color-workaround"
# The same problem also exists for GtkCList and GtkCTree
# Only match GtkCList and not the parent widgets, because that would also change the headers.
widget_class "*<GtkCList>" style "mist-fg-is-text-color-workaround"
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