This fork of the D3.js world countries tree displays a hierarchical dataset of countries organized by continent and subregion. The visualization uses a horizontal tree layout with branching links, and text labels whose font size decreases with depth to show the classification from "World" down to individual countries. The code builds the layout with `d3.tree()` and `d3.hierarchy()`, renders the links with `d3.linkHorizontal()`, and enables pan and zoom through a custom `zoom()` extension that applies transformations to a group element. Data is loaded from `data.json`, and the SVG output is styled with custom CSS.