Plugin front pages have jQuery error!

hi.
i installed plugin and in front page, have jQuery problem console!
also, in your demo version, you can see:
https://demo.wpschoolpress.com/sch-dashboard/

Uncaught ReferenceError: $ is not defined
at (index):255

$( document ).ready(function() {
ajax_url =’https://demo.wpschoolpress.com/wp-admin/admin-ajax.php’;
date_format=’mm/dd/yy’;
$(‘.content-wrapper’).on(‘click’,function(){
$(‘.control-sidebar’).removeClass(‘control-sidebar-open’);
});
$(‘body’).addClass(‘wpschoolpress’);
$(‘html’).removeClass(‘wp-toolbar’);
});

please help or update for resolve this problem, thanks alot <3

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