progress bar color change css

progress::-moz-progress-bar { background: black; }
progress::-webkit-progress-value { background: black; }
progress { color: black; }

var bar = new ProgressBar.Line('#container', {
    step: function(state, bar, attachment) {
        bar.path.setAttribute('stroke', state.color);
    }
});

var opts = {
    from: { color: '#000 '},
    to: { color: '#888'}
};
bar.animate(0.5, opts);