As @m3g4p0p says rather than use a button you can just use a regular hyperlink tag. Then style that with CSS to look like a button
For example this is one i use on my site (i don’t claim it to be perfect)
<style> /*Square grey Button */ .grey_btn_sqr:visited{ color:#fff; } .grey_btn_sqr { background-color:#666; text-indent:0px; display:inline-block; color:#ffffff; font-family:'Open Sans', Arial; font-size:15px; font-weight:bold; font-style:normal; height:auto; padding:0 10px; line-height:34px; width:auto; text-decoration:none; text-align:center; border:none; } .grey_btn_sqr:hover { color:#ffffff; background-color:#999; text-decoration:none; }.grey_btn_sqr:active { position:relative; top:1px; } </style>
then on your link you can just add that class
<a href="#" onclick="closeWin()" class="grey_btn_sqr">Close this window</a>
You could add that class to the button as well or any bit of text you want.
So you could use a span if you wanted i guess
<span onclick="closeWin()" class="grey_btn_sqr">Close this window</span>
But you’d prob need to add some extra styling to get the correct cursor etc so it appear like a link.