offset margin left to apply background color to comment area

src/client/styles/scss/_comment_growi.scss

@@ -33,7 +33,8 @@
   }
 
   .page-comments-row {
-    margin: 30px 0px;
+    // offset margin left to apply bg-color
+    margin: 30px 0px 30px -15px;
   }
 
   .page-comments {