Highlighting the selected category band on the X axis

HTML

<link rel="stylesheet" href="http://www.webdetails.pt/ctools/charts/lib/tipsy.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/require.js/2.1.19/require.min.js"></script>
<script src="//webdetails.github.io/ccc/charts/lib/amd/require.config.js"></script>
<script src="//webdetails.github.io/ccc/charts/lib/q01-01.js"></script>
<div id="cccExample" />

JavaScript

require([
  "ccc/pvc", 
  "ccc/def", 
  "ccc/protovis"
], function(pvc, def, pv) {

    var selectedCateg = "BMW";

    new pvc.BarChart({
        canvas: "cccExample",
        width:  700,
        height: 400,
        axisGrid:    true,
        orientation: "horizontal",
        extensionPoints: {
          plot_add: function() {
                // Shadow Panel
                return new pv.Panel()
                    .left(function() {
                        var baseScale = 
                              this.getContext().chart.axes.ortho.scale;
                        return baseScale(selectedCateg) -
                               baseScale.range().step / 2;
                    })
                    .width(function() {
                        var baseScale =
                              this.getContext().chart.axes.ortho.scale;
                        return baseScale.range().step;
                    })
                    .fillStyle('rgba(0,0,250, 0.3)');
            }
        }
    })
    .setData(relational_04, {crosstabMode: false })
    .render();
});