how to create simple pop-up in html and javascript

how to create simple pop-up  in html and javascript
there is the complete code of creating simple pup-up form.

    <script>
     function show(){ document.getElementById('my_id').style.display="block";}
     function hide(){ document.getElementById('my_id').style.display="none";}
    </script>

<div id="my_id" style="display:none;position: fixed;top: 27%;background: black;opacity: 0.6;left: 33%;color: white;">
<span style="float: right;color: white; cursor:pointer" onclick="hide()">close</span>
<form action="" method="post">
element of form
                        <input type="text" name="name" maxlength="100" value="" class="width257 formElement" id="name">
               
            </form>
            </div>