<input type=button value="Клик" onclick="toggle_show('Clk')"><div id="Clk" style="background:green;width:260px;height:170px;" "></div>
<script>
function toggle_show(id) {
var el=document.getElementById(id)
el.style.display = el.style.display == 'none' ? 'block' : 'none';
}
</script>