Do not leave silver color unset in Swimlane and List CSS

client/components/lists/list.css

@@ -356,7 +356,7 @@
   border-bottom: 6px solid #51e898;
 }
 .list-header-silver {
-  border-bottom: 6px solid unset;
+  border-bottom: 6px solid #e4e4e4;
 }
 .list-header-peachpuff {
   border-bottom: 6px solid #ffdab9;

client/components/swimlanes/swimlanes.css

@@ -157,7 +157,7 @@
   color: #4d4d4d !important;
 }
 .swimlane-silver {
-  background: unset !important;
+  background: #ccc !important;
   color: #4d4d4d !important;
 }
 .swimlane-peachpuff {