d3/examples/box/box.css

.boxplot .whisker, .boxplot .median { stroke: #000; stroke-width: 1.5px; }
.boxplot .box { stroke: #000; stroke-width: 1.5px; fill: #fff; }
.boxplot .center { stroke: #000; stroke-width: 1px; stroke-dasharray: 3 3; }
.boxplot .outlier { stroke: #666; stroke-width: .5px; fill: none; }