[evince] libview: Fix deprecation for getting background color

[Germán Poo-Caamaño <gpoo src gnome org>]

commit 42dca8588fed4f0f3a18b02395d422663aadafe7
Author: Germán Poo-Caamaño <gpoo gnome org>
Date:   Sun Jul 5 00:40:49 2020 -0400

    libview: Fix deprecation for getting background color

 libview/ev-view.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/libview/ev-view.c b/libview/ev-view.c
index 049074e6..e0171b4d 100644
--- a/libview/ev-view.c
+++ b/libview/ev-view.c
@@ -7401,12 +7401,18 @@ _ev_view_get_selection_colors (EvView  *view,
 
        context = gtk_widget_get_style_context (widget);
        gtk_style_context_save (context);
+       gtk_style_context_add_class (context, EV_STYLE_CLASS_FIND_RESULTS);
        state = gtk_style_context_get_state (context) |
                (gtk_widget_has_focus (widget) ? GTK_STATE_FLAG_SELECTED : GTK_STATE_FLAG_ACTIVE);
        gtk_style_context_set_state (context, state);
 
-       if (bg_color)
-               gtk_style_context_get_background_color (context, state, bg_color);
+       if (bg_color) {
+               g_autoptr (GdkRGBA) color = NULL;
+               gtk_style_context_get (context, state,
+                                      GTK_STYLE_PROPERTY_BACKGROUND_COLOR,
+                                      &color, NULL);
+               *bg_color = *color;
+       }
 
        if (fg_color)
                gtk_style_context_get_color (context, state, fg_color);