title: How to fill area with custom color under line in nvd3 linechart ?
body: <p>I'm working with nvd3 and I'm not much hands-on with its styling (css properties) to customize it. I have a line chart with two data lines on it.
  The code for drawing the lines is following:</p>
  
  <pre><code>nv.addGraph(function() {
          chart = nv.models.lineChart();
  
          chart.margin({
              left : 100,
              bottom : 100
          }).useInteractiveGuideline(true).showLegend(true).duration(250);
          chart.xAxis.axisLabel("Date").tickFormat(function(d) {
              var date = new Date(d);
              return d3.time.format("%b-%e")(date);
          });
          chart.yAxis.axisLabel('').tickFormat(d3.format(',.2f'));
  
          chart.showXAxis(true);
  
          d3.select('#startupRiskLineChart').datum(
                  prepareDataObj(val1_y, val1_x, val2_y, val1_x))
                  .transition().call(chart);
          ;
          nv.utils.windowResize(chart.update);
          chart.dispatch.on('stateChange', function(e) {
              nv.log('New State:', JSON.stringify(e));
          });
          return chart;
      });
  </code></pre>
  
  <p>Is there any way to fill the area under data line with a lighter color? 
  Any help would be highy apperiated.</p>