let us how it goes

<!DOCTYPE html>
<meta charset="utf-8">
<style>
 
svg {
  font: 10px sans-serif;
}
 
 
.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.y.axis path {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.brush .extent {
  stroke: #fff;
  fill-opacity: .125;
  shape-rendering: crispEdges;
}

.line {
  fill: none;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
 
var margin = {top: 10, right: 10, bottom: 100, left: 40},
    margin2 = {top: 430, right: 10, bottom: 20, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom,
    height2 = 500 - margin2.top - margin2.bottom;
 
var color = d3.scale.category10();
 
var parseDate = d3.time.format("%Y%m").parse;
 
var x = d3.time.scale().range([0, width]),
    x2 = d3.time.scale().range([0, width]),
    y = d3.scale.linear().range([height, 0]),
    y2 = d3.scale.linear().range([height2, 0]);
 
var xAxis = d3.svg.axis().scale(x).orient("bottom"),
    xAxis2 = d3.svg.axis().scale(x2).orient("bottom"),
    yAxis = d3.svg.axis().scale(y).orient("left");
 
var brush = d3.svg.brush()
    .x(x2)
    .on("brush", brush);
 
var line = d3.svg.line()
    .defined(function(d) { return !isNaN(d.temperature); })
    .interpolate("cubic")
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.temperature); });
 
var line2 = d3.svg.line()
    .defined(function(d) { return !isNaN(d.temperature); })
    .interpolate("cubic")
    .x(function(d) {return x2(d.date); })
    .y(function(d) {return y2(d.temperature); });
 
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom);
 
svg.append("defs").append("clipPath")
    .attr("id", "clip")
  .append("rect")
    .attr("width", width)
    .attr("height", height);
 
var focus = svg.append("g")
  .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
      
var context = svg.append("g")
  .attr("transform", "translate(" + margin2.left + "," + margin2.top + ")");
 
d3.csv("test.csv", function(error, data) {
 
  color.domain(d3.keys(data[0]).filter(function(key) { return key !== "date"; }));
 
    data.forEach(function(d) {
      d.date = parseDate(d.date);
    });
 
  var sources = color.domain().map(function(name) {
      return {
        name: name,
        values: data.map(function(d) {
          return {date: d.date, temperature: +d[name]};
        })
      };
    });
 
    x.domain(d3.extent(data, function(d) { return d.date; }));
    y.domain([d3.min(sources, function(c) { return d3.min(c.values, function(v) { return v.temperature; }); }),
              d3.max(sources, function(c) { return d3.max(c.values, function(v) { return v.temperature; }); }) ]);
    x2.domain(x.domain());
    y2.domain(y.domain());
    
    var focuslineGroups = focus.selectAll("g")
        .data(sources)
      .enter().append("g");
      
    var focuslines = focuslineGroups.append("path")
        .attr("class","line")
        .attr("d", function(d) { return line(d.values); })
        .style("stroke", function(d) {return color(d.name);})
        .attr("clip-path", "url(#clip)");
    
    focus.append("g")
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height + ")")
        .call(xAxis);
 
    focus.append("g")
        .attr("class", "y axis")
        .call(yAxis);
        
    var contextlineGroups = context.selectAll("g")
        .data(sources)
      .enter().append("g");
    
    var contextLines = contextlineGroups.append("path")
        .attr("class", "line")
        .attr("d", function(d) { return line2(d.values); })
        .style("stroke", function(d) {return color(d.name);})
        .attr("clip-path", "url(#clip)");
 
    context.append("g")
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height2 + ")")
        .call(xAxis2);
 
    context.append("g")
        .attr("class", "x brush")
        .call(brush)
      .selectAll("rect")
        .attr("y", -6)
        .attr("height", height2 + 7);
        
        
});
 
function brush() {
  x.domain(brush.empty() ? x2.domain() : brush.extent());
  focus.selectAll("path.line").attr("d",  function(d) {return line(d.values)});
  focus.select(".x.axis").call(xAxis);
  focus.select(".y.axis").call(yAxis);
}
 
</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js