jsxgraph axis and label opacity

HTML

<link rel="stylesheet" href="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraph.css">
<script src="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraphcore.js"></script>
<div id='box' class='jxgbox'></div>

CSS

#box {
    width:500px;
    height:500px;
}

JavaScript

var board = JXG.JSXGraph.initBoard('box', {boundingbox: [-10, 10, 10, -10]});
var N = board.create('slider', [[0,1.5],[3,1.5],[1,3,40]], {name:'n',snapWidth:1});
 

var c = board.create('curve', [[0],[0]],{strokecolor:'red', strokeWidth:2});
c.updateDataArray = function() {
        var r = 1, n = Math.floor(N.Value()),
            x = [0], y = [0],
            phi = Math.PI/n,
            h = r*Math.cos(phi),
            s = r*Math.sin(phi),
            i, j,
            px = 0, py = 0, sgn = 1,
            d = 16,
            dt = phi/d,
            pt;

        for (i = 0; i < n; i++) {
            for (j = -d; j <= d; j++) {
                pt = dt*j;
                x.push(px + r*Math.sin(pt));
                y.push(sgn*r*Math.cos(pt) - (sgn-1)*h*0.5);
            }
            px += s;
            sgn *= (-1);
        }
        x.push((n - 1)*s);
        y.push(h + (sgn - 1)*h*0.5);
        this.dataX = x;
        this.dataY = y;
    }