[gnome-games/wip/exalm/headerbar] css: Make headerbar in fullscreen transparent

[Alexander Mikhaylenko <alexm src gnome org>]

commit ceaad6346e4dca9c3706cdc046caee01563a0fc8
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Mon Jun 8 22:35:27 2020 +0500

    css: Make headerbar in fullscreen transparent

 data/gtk-style.css | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
---
diff --git a/data/gtk-style.css b/data/gtk-style.css
index a5d7f27e..539ff330 100644
--- a/data/gtk-style.css
+++ b/data/gtk-style.css
@@ -112,3 +112,25 @@ list.rounded:backdrop,
 list.separators row:not(:last-child) {
        border-bottom: 1px solid rgba(0, 0, 0, 0.15);
 }
+
+window.fullscreen {
+  background: black;
+}
+
+window.fullscreen headerbar {
+  color: #EEEEEC;
+  border-color: alpha(#070707, .75);
+  background:
+    alpha(#353535, 0)
+    cross-fade(0% -gtk-icontheme("system-run-symbolic"), image(transparent)) 90% 0/256px 256px no-repeat,
+    linear-gradient(to top, alpha(#262626, .75), alpha(#2b2b2b, .75));
+}
+
+window.fullscreen headerbar:backdrop {
+  color: #919190;
+  border-color: alpha(#202020, .75);
+  background:
+    alpha(#353535, 0)
+    cross-fade(0% -gtk-icontheme("system-run-symbolic"), image(transparent)) 90% 0/256px 256px no-repeat,
+    image(alpha(#353535, .75));
+}