-moz-transition: all 400ms ease-in; -ms-transition: all 400ms ease-in; -o-transition: all 400ms ease-in; transition: all 400ms ease-in; } .hidden-wrapper.off { height: 0; opacity: 0; } .hidden-wrapper:not(.off) { height: auto; opacity: 1; } </style> <?php $form->printIncludes('css'); ?> </head> <body> <h1 class="text-center">Contact Form 3</h1> <div class="container"> <div class="row"> <div class="col-sm-10 col-sm-offset-1 col-md-8 col-md-offset-2"> <?php if (isset($sent_message)) { echo $sent_message; } $form->render(); ?> </div> </div>