Add pulsate/flash animations for drawing attention to posts

framework/core/js/forum/src/components/stream-content.js

@@ -179,16 +179,33 @@ export default class StreamContent extends mixin(Component, evented) {
   scrollToItem($item, noAnimation) {
     var $container = $('html, body').stop(true);
     if ($item.length) {
-      var scrollTop = $item.is(':first-child') ? 0 : $item.offset().top - this.getMarginTop();
-      if (noAnimation) {
-        $container.scrollTop(scrollTop);
-      } else if (scrollTop !== $(document).scrollTop()) {
-        $container.animate({scrollTop: scrollTop}, 'fast');
+      var itemTop = $item.offset().top - this.getMarginTop();
+      var itemBottom = itemTop + $item.height();
+      var scrollTop = $(document).scrollTop();
+      var scrollBottom = scrollTop + $(window).height();
+
+      // If the item is already in the viewport, just flash it, we don't need to
+      // scroll anywhere.
+      if (itemTop > scrollTop && itemBottom < scrollBottom) {
+        this.flashItem($item);
+      } else {
+        var scrollTop = $item.is(':first-child') ? 0 : itemTop;
+        if (noAnimation) {
+          $container.scrollTop(scrollTop);
+        } else if (scrollTop !== $(document).scrollTop()) {
+          $container.animate({scrollTop: scrollTop}, 'fast', this.flashItem.bind(this, $item));
+        } else {
+          this.flashItem($item);
+        }
       }
     }
     return $container.promise();
   }
 
+  flashItem($item) {
+    $item.addClass('flash').one('animationend webkitAnimationEnd', () => $item.removeClass('flash'));
+  }
+
   /**
     Find the DOM element of the item that is nearest to a post with a certain
     number. This will either be another post (if the requested post doesn't

framework/core/less/forum/discussion.less

@@ -166,6 +166,18 @@
     background: @fl-primary-color;
   }
 }
+@-webkit-keyframes pulsate {
+  0% {transform: scale(1)}
+  50% {transform: scale(1.02)}
+  100% {transform: scale(1)}
+}
+.item.pulsate {
+  -webkit-animation: pulsate 1s ease-in-out;
+  -webkit-animation-iteration-count: infinite;
+}
+.item.flash {
+  -webkit-animation: pulsate 0.2s ease-in-out;
+  -webkit-animation-iteration-count: 1;
 }
 .post-header {
   margin-bottom: 10px;