First, make sure you download the slick library from the link you provided. The "/ slick" folder should be in the same directory as your HTML code.
Add the following lines to <head>
<link rel="stylesheet" type="text/css" href="slick/slick-theme.css"/> <link rel="stylesheet" type="text/css" href="slick/slick.css"/>
Add these lines to <body> to import the library
<script type="text/javascript" src="http://code.jquery.com/jquery-1.11.0.min.js"></script> <script type="text/javascript" src="slick/slick.min.js"></script>
Then your code should be:
<script> resizeWindow(); window.addEventListener('resize', resizeWindow); function resizeWindow(){ $('.slider').slick({ responsive: [ { breakpoint: 2500, settings: "unslick" }, { breakpoint: 640, settings: { dots: true } } ] }); } </script>
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