[gnome-usage] css: Update background of graph

[Felipe Borges <felipeborges src gnome org>]

commit 4b0cf7b3973029851de2aeb3f04253eb3c1294f8
Author: Petr Štětka <pstetka redhat com>
Date:   Thu Mar 15 18:12:07 2018 +0100

    css: Update background of graph
    
    In dark theme (adwaita) white bachground of graph is ugly.
    This commit change background of graph for correct color in dark theme.

 data/interface/adwaita.css | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/data/interface/adwaita.css b/data/interface/adwaita.css
index 7a75efa..c5c38ed 100644
--- a/data/interface/adwaita.css
+++ b/data/interface/adwaita.css
@@ -52,9 +52,8 @@ button.graph-switcher {
 }
 
 rg-graph.big {
-    background-color: #ffffff;
     background-size: 57px 57px;
-    background-image: repeating-linear-gradient(0deg, #e6e6e6, #e6e6e6 1px, transparent 1px, transparent 
57px);
+    background-image: repeating-linear-gradient(0deg, alpha(@theme_fg_color, 0.2), alpha(@theme_fg_color, 
0.2) 1px, transparent 1px, transparent 57px);
 }
 
 rg-graph.line {