datepicker not working

Hi there,

I am trying to build a simple form using also the datepicker
This is what I include into my standard page:

<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<link rel="stylesheet" href="/resources/demos/style.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
<script>
$( function() {
$( "#datepicker" ).datepicker();
} );
</script>
<form>
<input type="text" id="datepicker" name="arrival_date">
</form>

But when I click on the field the date pop-up does not as usual appear next to the field, it appears at the very top of the page (screenshot – you need to scroll up since that field is pretty much down the page) and it’s in an unreadable format… I used this code before in other themes without any problem.

I also tried https://www.ads-software.com/plugins/wp-datepicker/ without any success… ??

Do you know a good fix for this?

Thank you,
Marc