title: pygal rendering png/svg black pictures
body: <p>I am using python (with a virtual env in LinuxMint), I installed <code>pygal</code>.</p>
  
  <p>Everything works fine (rendering to html) but not rendering to svg or png .
  The result : Nothing but a black background.</p>
  
  <p>I installed <code>cssselect</code> and <code>tinycss</code> like mentioned <a href="https://github.com/Kozea/pygal/issues/2">here</a> .</p>
  
  <p>It works for the first time, but when retrying, I had the same issue .</p>
  
  <p>(I don't know if this is related or not, but this happens to me when exporting a photo using darktable last week)</p>
  
  <p>I use the example from the website of pygal:</p>
  
  <pre><code>import pygal                                                       # First import pygal
  bar_chart = pygal.Bar()                                            # Then create a bar graph object
  bar_chart.add('Fibonacci', [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55])  # Add some values
  bar_chart.render_to_file('bar_chart.svg')                          # Save the svg to a file
  </code></pre>
  
  <p><strong>EDIT:</strong></p>
  
  <pre><code>bar_chart.render_to_png('bar_chart.png')
  </code></pre>
  
  <p>is working now .</p>
  
  <p>But not:</p>
  
  <pre><code>bar_chart.render_to_file('bar_chart.svg')
  </code></pre>