Fix issue #132: Challenge Listings: Minor styling bugs at the XXS (<320px) sreen size

Author: elfman

src/shared/components/challenge-listing/Filters/ChallengeFilters.scss

@@ -10,6 +10,9 @@
     padding: 0 $base-unit * 4;
 
     @include xxs-to-sm {
+      display: flex;
+      justify-content: space-between;
+      flex-wrap: wrap;
       padding: 0 $base-unit * 3;
     }
   }

src/shared/components/challenge-listing/Filters/FiltersPanel/style.scss

@@ -130,6 +130,7 @@ $panel-radius-4: $corner-radius * 2;
 
     @include xxs-to-sm {
       display: block;
+      margin-right: 0;
     }
   }