How do I keep an overlay open by default with Javascript? -

hey guys have login overlay following code:

<!-- overlay --> <div id="mynav" class="overlay">  <!-- login goes here -->  <!-- end login --> </div>  <!-- use element open/show overlay navigation menu --> <span onclick="opennav()">open</span> 

i'm using javascript open it, , removed close button.

<script type="text/javascript">  function opennav() {     document.getelementbyid("mynav").style.width = "100%"; }  /* close when clicks on "x" symbol inside overlay */ function closenav() {     document.getelementbyid("mynav").style.width = "0%"; }  </script> 

my question how keep default set open? thank in advance.

well if understand problem.... , how css setup...

with old css

#mynav {  width:100%; } 

that way 100% when page loads , manage width user interaction in javascript.