fixed kanban css

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

web/src/main/resources/web/css/default-color.css

@@ -96,7 +96,7 @@ tr:hover a{
 
 .kanban .state_10 .box,
 .kanban .state_100 .box{
-    background: linear-gradient(rgba(0,0,0,0.6));
+    opacity: 0.5;
 }
 
 .kanban .state_10 .box,
@@ -262,4 +262,4 @@ tr:hover a{
 
 .vcard span.inactive{
     color: #222200;
-}
+}