step7.js

chartContainer
  .append('g')
    .attr('class', 'x axis')
    .attr('transform', 'translate(0,' + height + ')')
    .style('storke', '#000')
    .call(d3.axisBottom(x));

chartContainer
  .append('g')
    .attr('class', 'y axis')
    .call(d3.axisLeft(y))
    .append('text')
    .attr('fill', '#000')
    .style('storke', '#000')
    .attr('transform', 'rotate(-90)')
    .attr('y', 6)
    .attr('dy', '.71em')
    .attr('text-anchor', 'end')
    .text('Data meaning');