TP3-transparent-area

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    
		svg {
  		font: 10px sans-serif;
		}

.line {
      fill: none;
      stroke: black;
      stroke-width: 2px;
    }
    
    .area {
      fill: pink;
    }
  </style>
</head>

<body>
  <script>
    
  var margin = {top: 80, right: 30, bottom: 20, left: 100},
      width = 760 - margin.left - margin.right,
      height = 400 - margin.top - margin.bottom;
    
  var svg = d3.select("body").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var parseDate = d3.timeParse("%b %Y");

var x = d3.scaleTime().range([0, width]),
    y = d3.scaleLinear().range([height, 0]),
    c = d3.scaleOrdinal(d3.schemeCategory10);
var stack = d3.stack();
	var area = d3.area()
    .curve(d3.curveBasis)
    .x(function(d) { return x(d.date); })
  	.y0(height)
    .y1(function(d) { return y(d.price); });
    
  d3.text('data.csv', function(error, raw) {

var dsv = d3.dsvFormat(',')
    var data = dsv.parse(raw);
    
    // Nest stock values by symbol.
    var symbols = d3.nest()
        .key(function(d) { return d.symbol; })
        .entries(data);

// Parse and caculate some values for each symbols
    symbols.forEach(function(s) {
      s.values.forEach(function(d) { 
        d.date = parseDate(d.date); 
        d.price = +d.price; 
      });
      
      s.maxPrice = d3.max(s.values, function(d) { return d.price; });
      s.sumPrice = d3.sum(s.values, function(d) { return d.price; });
      
      console.log(symbols);
    });
    		 
    x.domain(d3.extent(data, function(d) { return d.date; }));
    y.domain([0, d3.max(symbols.map(function(d) { return d.maxPrice; }))]);

svg.selectAll(".line").data(symbols).enter()
      	.append("path")
    		.attr("class", "line")
        .attr("d", function(d) { return area(d.values); })
    		.style("stroke", function(d) { return c(d.key); });
    
    svg.selectAll(".line").data(symbols).enter()
      	.append("path")
    		.attr("class", "area")
    		.style("fill", function(d) { return color[counter++];})
    		.style("opacity", 0.2)
        .attr("d", function(d) { return area(d.values); })
    		.style("stroke", function(d) { return c(d.key); });

svg.append("g")
        .attr("class", "axis axis--y")
        .call(d3.axisLeft(y).ticks(20));
    
    svg.append("g")
        .attr("class", "axis axis--x")
        .attr("transform", "translate(0," + height + ")")
        .call(d3.axisBottom(x));

var legend = svg.selectAll(".legend")
    .data(c.domain())
  	.enter().append("g")
    .attr("class", "legend")
    .attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });

legend.append("rect")
      .attr("x", 30)
      .attr("width", 18)
      .attr("height", 18)
      .style("fill", c);

legend.append("text")
      .attr("x", 50)
      .attr("y", 9)
      .attr("dy", ".35em")
      .style("text-anchor", "start")
      .text(function(d) { return d; });
    
  });
    
  var color = ["blue","orange","green","red"];
  var counter = 0;
  </script>
</body>

https://d3js.org/d3.v4.min.js