Update color of outdated packages in dark theme

install/deb/themes/dark.css

@@ -502,7 +502,7 @@ div.l-content > div.l-separator:nth-of-type(4) {
 
 .units .l-unit.l-unit--outdated {
   color: #d4d4d4;
-  background-color: #760000;
+  background-color: #981111;
 }
 
 .l-unit--outdated.selected {