Plot.plot({
x: {axis: "top"},
y: {domain: [0, d3.max(transit, d => d.count) / (overlap + 1)]},
axis:null,
marks:[
Plot.areaY(transit, {x:'period', y:'count', fy:'state', curve: "basis", fill: "#ddd"}),
Plot.lineY(transit, {x:'period', y:'count', fy:'state', curve: "basis", stroke: "#000"}),
Plot.text(transit, Plot.selectFirst({x: d3.min(transit, d => d.period), fy: "state", text: "state", dx: -3, frameAnchor: "right"}))
]
})