获取当前屏幕高度并赋值到对应的标签

<script>
	var div_height = window.screen.availHeight;
	$(".login_aa").height(div_height);
</script>

获取当前屏幕高度，并减去100px，然后赋值到对应的标签

<script>
	var div_height = window.screen.availHeight;
	var height = div_height - 100;
	$(".login_aa").height(height);
</script>