When zoomming the chart, the y-aixs can't read clearly, so I think add a "backgorund" for y-axis will be more readable when zoom the chart ```js svg.append("g") .attr("class", "x-axis") .call(xAxis); // add a white rect as the y-axis background before generate the y-axis svg.append('rect') .attr('x', 0) .attr('y', 0) .attr('width', margin.left) .attr('height', height) .attr('fill', 'white') svg.append("g") .attr("class", "y-axis") .call(yAxis); ```