tidy up active state

opentech/static_src/src/app/src/components/SubmissionsByRoundList.scss

@@ -26,8 +26,8 @@ $listing-header-height: 75px;
         @include submission-list-item;
 
         &.is-active {
-            border-right: 0;
-            border-left: 0;
+            border-right: 2px solid $color--white;
+            transition: border $transition;
         }
 
         &--heading {

opentech/static_src/src/sass/apply/abstracts/_mixins.scss

@@ -158,5 +158,4 @@
 @mixin submission-list-item {
     border-bottom: 2px solid $color--light-mid-grey;
     border-right: 2px solid $color--light-mid-grey;
-    border-left: 2px solid $color--light-mid-grey;
 }