_sass: Add top margin to abstract-card

_sass/custom/mixins.scss

 @mixin abstract-card() {
   box-shadow: 0 1px 3px rgba(0, 0, 0, 0.07), 0 4px 14px rgba(0, 0, 0, 0.05);
-  margin-left: -$gutter-spacing-sm;
-  margin-right: -$gutter-spacing-sm;
-  margin-bottom: $sp-4;
+  margin: $sp-4 -$gutter-spacing-sm;
 
   @include mq(md) {
     border-radius: $border-radius;
-    margin-left: 0;
-    margin-right: 0;
+    margin: $sp-4 0;
   }
 }