[bes]

<button style="position: absolute; left: 0px; top: 0px">click</button>
<script>
document.body.children[0].onclick = function () {
	document.body.style.cssText = 'position: absolute; left: 20px; top: 20px;';
	document.body.insertAdjacentHTML('afterBegin', '<button style="position: fixed; left: 0px; top: 0px">button</button>');
}
</script>