title: radio button in conjunction with c3 does not show text
body: <p>I am creating a custom legend, that contains radio inputs, of a pie chart  created with c3.
  I create radio inputs via D3 API. 
  I haven't been able to show the text on the side of radio input.</p>
  
  <pre><code>d3.select('.container').insert('div', '.chart')
     .selectAll('input')
     .data(['data', 'data10', 'data5'])
     .enter().append('input')    
     .attr('type', function (id) { return 'radio'; })
     .attr('name', function (id) { return id;})
     .attr('value', function (id) { return id;})
     .append('span')
     .html(function (id) { return id; });
  </code></pre>
  
  <p>Here is the css:</p>
  
  <pre><code>input{
      width:31.5%;    
  }
  input span{    
      color:red;
      background-color: green;
  }
  </code></pre>
  
  <p>None of it has any effect. Here is my <a href="http://jsfiddle.net/agcsi/1vk25ma8/3/" rel="nofollow">full jsfiddle</a>.
  Any idea what I am doing wrong?</p>