ange: " + d.x0 + " - " + d.x1)
      .style("left", (d3.mouse(this)[0]+20) + "px")
      .style("top", (d3.mouse(this)[1]) + "px")
  }
  var moveTooltip = function(d) {
    tooltip
    .style("left", (d3.mouse(this)[0]+20) + "px")
    .style("top", (d3.mouse(this)[1]) + "px")
  }
  // A function that change this tooltip when the leaves a point: just need to set opacity to 0 again
  var hideTooltip = function(d) {
    tooltip
      .transition()
      .duration(100)
      .style("opacity", 0)
  }

  // appen