A histogram displays the distribution of a dataset of numeric values, with bars colored on a gradient from light to dark steelblue based on frequency. A black kernel density estimation curve overlays the bars, and users can adjust both the number of histogram bins and the bandwidth of the Gaussian kernel via range sliders, triggering smooth transitions. The visualization is built with D3 v4, using `d3.histogram`, `d3.layout.histogram`, `d3.scale.linear`, and SVG rendering, with the density curve computed via a custom `kernelDensityEstimator` and drawn using `d3.line` with `d3.curveBasis`.