Counties of Croatia (from '92. to '97.)

<!DOCTYPE html>
<meta charset="utf-8">
<style>
/*path {
  fill: none;
  stroke: #000;
  stroke-linejoin: round;
  stroke-linecap: round;
}
*/

.subunit {
  fill: #777;

}

.country {
  stroke: #fff;
  fill: none;
}
/*

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<script>

var width = 960,
    height = 600;

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

d3.json("croatiatopo.json", function(error, cro) {
  if (error) return console.error(error);

var subunits = topojson.feature(cro, cro.objects.croatia);

var projection = d3.geo.mercator()
    .center([15, 37.5]) // x to left, y to bottom
    .scale(5400)
    .translate([width / 3, height * 2]);

var path = d3.geo.path()
    .projection(projection);

zupanije = svg.selectAll(".subunit")
    .data(topojson.feature(cro, cro.objects.croatia).features)
  .enter().append("path")
    .attr("class", function(d) { /* console.log(d);*/ return "subunit " + d.properties.HASC_1.substr(3,2); }) //str.substr(start[, length])
    .attr("d", path);

zupanije.append("title")
      .text(function(d, i) { return d.properties.NAME_1; });

zupanije.on("mouseover", function (d, i) {

d3.select(this).style("fill", "steelblue"); // .attr("transform", "translate(5,5)");

//console.log(d.properties.NAME_1);
  });

zupanije.on("mouseout", function (d, i) {

d3.select(this).style("fill", "#777");

});

svg.append("path")
    .datum(subunits)
    .attr("d", path)
    .attr("class", "country");

});

d3.select(self.frameElement).style("height", height + 80 + "px");

</script>

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

Modified http://d3js.org/topojson.v1.min.js to a secure url

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

https://d3js.org/topojson.v1.min.js