GWD does not support events on native HTML elements in the Events panel in this release. Events are supported in the UI only for Components. However, it is fairly simple to add an event using the Code view. I have attached an example.
I drew a DIV using GWD, switched to Code view and added
<script>
document.querySelector('.gwd-div-sqhx').addEventListener('mouseover', function() {
console.log('mouse over event on div');
});
</script>
just above the </body> tag.
Please let us know if this does not work for you.
Events for native HTML elements is something we are looking into for a future release.
~ Kishore (GWD Engineer)