tooltip = d3
.select('body')
.append('div')
.attr('class', 'd3-tooltip')
.style('position', 'absolute')
.style('z-index', '10')
.style('visibility', 'hidden')
.style('padding', '10px')
.style('background', 'rgba(0,0,0,0.6)')
.style('border-radius', '4px')
.style('color', '#fff')
.style('font-size', "18px")
.style('font-weight', 250)
.style('font-family', 'FreeMono, monospace')
.text('a simple tooltip')