add mark as read button

src/app/components/shared/comment-list/comment-list.component.scss

@@ -3,7 +3,7 @@ mat-card {
   background-color: #b2ebf2;
 }
 
-mat-card-content>:first-child {
+mat-card-content > :first-child {
   margin-top: 20px;
 }
 
@@ -16,3 +16,7 @@ mat-toolbar {
 .outer-card {
   border-radius: 8px;
 }
+
+.btn-right {
+  float: right;
+}