xxxxxxxxxx<title>blockup</title><body style='width:720px'> <p style='text-align: center;'> <button id='start'>Start</button> <button id='shuffle'>Shuffle</button> <p> <script src='https://d3js.org/d3.v4.min.js'></script> <script src='script.js'></script></body> https://d3js.org/d3.v4.min.js