Add font-family override for previewer

core/css/tabbed-container.css

@@ -148,4 +148,8 @@
 .tabbed-container._weditor .box[name="edit"] textarea {
 	border: none;
 	margin: 0px;
+}
+
+.tabbed-container._weditor .box[name="preview"] {
+	 font-family: initial;
 }