smoother comment form expansion

lms/static/coffee/src/discussion/views/thread_response_view.coffee

@@ -36,14 +36,20 @@ if Backbone?
     hideEditorChrome: ->
       @$('.wmd-button-row').hide()
       @$('.wmd-preview').hide()
-      @$('.wmd-input').css(height: '50px')
+      @$('.wmd-input').css({
+        height: '35px',
+        padding: '0'
+      })
       @$('.comment-post-control').hide()
 
     showEditorChrome: ->
       @$('.wmd-button-row').show()
       @$('.wmd-preview').show()
       @$('.comment-post-control').show()
-      @$('.wmd-input').css(height: '125px')
+      @$('.wmd-input').css({
+        height: '125px',
+        padding: '10px'
+      })
 
     renderComments: ->
       comments = new Comments()

lms/static/sass/_discussion.scss

@@ -1538,6 +1538,10 @@ body.discussion {
   .comment-form {
     padding: 8px 20px;
 
+    .wmd-input {
+      @include transition(all .2s);
+    }
+
     .wmd-button {
       background: transparent;