Style required question submit error

www/form/app-form.less

@@ -308,6 +308,10 @@
                                 color: @cryptpad_color_link;
                             }
                         }
+                        .alert-danger {
+                            font-size: 1rem;
+                            padding: 10px;
+                        }
                     }
                     .cp-form-anon-answer {
                         text-align: center;

www/form/inner.js

@@ -2500,8 +2500,10 @@ define([
                 });
                 var list = h('ul', lis);
                 var divContent = [
-                    h('span', Messages.form_requiredWarning),
-                    list
+                    h('div.alert.alert-danger', [
+                        Messages.form_requiredWarning,
+                        list
+                    ])
                 ];
                 $errors.empty().append(divContent);
             });