--- a/static/candolint.js	Sat Sep 23 13:00:12 2017 +0800
+++ b/static/candolint.js	Sat Sep 23 13:07:47 2017 +0800
@@ -120,6 +120,25 @@
                 .attr('cx', function(d) { return x(d.ordinal); })
                 .attr('cy', function(d) { return series.axis(d[series.name]); });
         });
+
+        var rectW = x.step();
+        g.append('g')
+            .attr('fill-opacity', 0)
+            .selectAll('rect')
+            .data(data.points)
+        .enter()
+            .append('rect')
+            .attr('x', function(d) { return x(d.ordinal) - rectW / 2 + 0.5; })
+            .attr('y', -margin.top)
+            .attr('height', height + margin.top + margin.bottom)
+            .attr('width', rectW)
+            .on('mouseover', function(d) {
+                var hx = x(d.ordinal) + 0.5;
+                hover.attr('opacity', 1).attr('x1', hx).attr('x2', hx);
+            })
+            .on('mouseout', function(d) {
+                hover.attr('opacity', 0);
+            });
     };
     $(window).on('resize', function() {
         if (+svg.attr('width') !== $container.width()) {