title: Make SVG transparent with d3 on leaflet
body: <p>I am following Mike Bostock's <a href="https://bost.ocks.org/mike/leaflet/" rel="nofollow noreferrer">tutorial</a> on how to display a <code>(geo)json</code> on a <code>leaflet map</code> through <code>d3</code>.</p>
  
  <p>It works - sort of. 
  When I try to display this file <a href="http://eric.clst.org/Stuff/USGeoJSON" rel="nofollow noreferrer">here</a> (the geoJSON "US States") I get a black block on my map isntead of the outlines of the states.<a href="https://i.stack.imgur.com/rS8ui.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rS8ui.png" alt="screenshot"></a></p>
  
  <p>Any ideas why?</p>