Added mixin to handle media queries that span multiple breakpoints

scss/mixins/_breakpoints.scss

@@ -74,3 +74,13 @@
     }
   }
 }
+
+// Media that spans multiple breakpoint widths.
+// Makes the @content apply between the min and max breakpoints
+@mixin media-breakpoint-between($lower, $upper, $breakpoints: $grid-breakpoints) {
+  @include media-breakpoint-up($lower, $breakpoints) {
+    @include media-breakpoint-down($upper, $breakpoints) {
+      @content;
+    }
+  }
+}