createTooltip = function(el) {
el
.style("position", "absolute")
.style("pointer-events", "none")
.style("top", 0)
.style("opacity", 0)
.style("background", "white")
.style("border-radius", "5px")
.style("box-shadow", "0 0 10px rgba(0,0,0,.25)")
.style("padding", "10px")
.style("line-height", "1.3")
.style("font", "11px sans-serif")
}