common/static/common/styles/studio/_custom.sass

@@ -670,12 +670,27 @@ button,
   .training-group-item
     +padding(3, x)
 
-  .training-group-item-content
+    &:last-child
-    @extend .box
+      +media-xl
+        padding-right: 0
 
-    background-color: var(--color-bg-tertiary)
+  .training-group-item-content
     width: var(--training-group-item-content-width)
 
+    .box
+      background-color: var(--color-bg-tertiary)
+
+      .comment-input-div
+        &.form-control
+          background-color: var(--color-bg-primary)
+
+      .replies
+        .comment
+          background-color: var(--color-bg-secondary)
+
+      .top-level-comment
+        background-color: var(--color-bg-primary)
+
   // TODO: revise training-group-item-nav display toggle on medium and small screens
   .training-group-item-nav
     +margin(3, bottom)

training/templates/training/section.html

@@ -51,6 +51,7 @@
     {% endif %}
   </div>
   <div class="training-group-item training-group-item-content">
+    <div class="box">
       <div class="row">
         <div class="col">
           <div class="row">
@@ -95,6 +96,7 @@
         </div>
       </div>
     </div>
+  </div>
 {% endblock nexted_content %}
 
 {% block scripts %}