[iagno] Bump Gtk+ required version to 3.20.

[Arnaud B. <arnaudb src gnome org>]

commit c477e0cc63e6fd6dcc0b5d112ac2d065b46df8e3
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Mon Feb 4 18:57:13 2019 +0100

    Bump Gtk+ required version to 3.20.
    
    And clean a bit the CSS.

 data/iagno.css | 27 +++++++++++++++------------
 meson.build    |  2 +-
 2 files changed, 16 insertions(+), 13 deletions(-)
---
diff --git a/data/iagno.css b/data/iagno.css
index bd54d57..c263b58 100644
--- a/data/iagno.css
+++ b/data/iagno.css
@@ -16,43 +16,46 @@
  * with this application. If not, see <http://www.gnu.org/licenses/>.
  */
 
-/* GtkXyz is pre-3.19.n */
-
 /* Labels' tweaks */
-GtkLabel.bold-label,
 label.bold-label {
   font-weight: bold;
 }
-GtkLabel.italic-label,
 label.italic-label {
   font-style: italic;
 }
-GtkGrid#scoreboard GtkLabel {
-  padding: 5px 2px;
-}
 grid#scoreboard label {
   padding: 4px 7px 4px 0;
 }
 
 /* Themes' dialog listbox */
-GtkListBox#themes-listbox GtkImage,
 list#themes-listbox image {
   transition-duration: 200ms;
   opacity: 0;
 }
 
-/* if you removed the fix at the bottom of the CSS file,
-   replacing "*" by "GtkImage" makes bug #746210 appear */
-GtkListBox#themes-listbox GtkListBoxRow:selected *,
 list#themes-listbox row:selected * {
   opacity: 1;
   color:@theme_selected_fg_color;
 }
-GtkListBox#themes-listbox GtkListBoxRow:selected GtkImage:backdrop,
 list#themes-listbox row:selected image:backdrop {
   color:@theme_unfocused_selected_fg_color;
 }
 
+/* make all widgets change font-size at same time */
+label.bold-label,
+button,
+headerbar,
+popover modelbutton {
+  transition:all       0    ease,
+             font-size 0.3s ease,
+             padding   0.3s ease,
+             margin    0.3s ease;
+}
+
 /* bug #746210: HighContrast doesn't update correctly on ListBoxRow selection
    hicolor is preserved because of a "*:selected *:link:visited" declaration */
 #fake-example *:selected *:visited { opacity: 1; }
+
+/*\
+* * the end
+\*/
diff --git a/meson.build b/meson.build
index a560e8a..dbfcd94 100644
--- a/meson.build
+++ b/meson.build
@@ -14,7 +14,7 @@ canberra_dependency = dependency('libcanberra')
 canberra_gtk3_dependency = dependency('libcanberra-gtk3', version: '>= 0.26')
 gio_dependency = dependency('gio-2.0', version: '>= 2.40.0')
 glib_dependency = dependency('glib-2.0', version: '>= 2.40.0')
-gtk_dependency = dependency('gtk+-3.0', version: '>= 3.15.0')
+gtk_dependency = dependency('gtk+-3.0', version: '>= 3.20.0')
 posix_dependency = meson.get_compiler('vala').find_library('posix')
 rsvg_dependency = dependency('librsvg-2.0', version: '>= 2.32.0')