HTML

Javascript (External JS libraries are required. Deploy to JSFiddle to see.)

CSS

Try it on JSFiddle! https://cdnjs.cloudflare.com/ajax/libs/d3/4.2.1/d3.min.js,http://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.20/topojson.min.js,http://code.jquery.com/ui/1.11.4/jquery-ui.js,http://www.brunelvis.org/js/brunel.2.3.min.js,http://www.brunelvis.org/js/brunel.controls.2.3.min.js,http://www.brunelvis.org/js/brunel.2.3.css,http://code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css,http://www.brunelvis.org/js/sumoselect.css