Test test test <br>
<form id="login_form">
<input type="text" value="Test">
<br><br>
<a href="#" id="close_login_form">
Закрыть форму
</a>
</form>
<br>
Test test test
<script type="text/javascript">
$(document).on("click", "#close_login_form", function(elem){
elem.preventDefault();
$("#login_form").slideUp(500);
});
</script>