This example demonstrates how D3’s `select()` and `selectAll()` methods locate and modify SVG elements, showing a simple bar chart whose rectangles change fill colors through chained attribute, style, and class updates. The code uses the D3 v7 library to select the `<rect>` elements by ID and class, then applies a chain of changes to the middle bar—such as setting its height, fill, and highlight class—while also updating the page title text. Console logs reveal the values read back from selected nodes, and the script prints the chart's bounding rectangle and SVG bounding box to inspect its layout.