Customizing Axes
This horizontal bar chart displays the top 10 most populous countries based on 2018 United Nations estimates, with a customized D3 v5 axis design. The vertical axis labels are left intact while the axis line and tick marks are removed, and the horizontal axis uses a custom tick format (converting G to B for billions) with grid lines extending across the plot. The chart uses `d3.scaleLinear`, `d3.scaleBand`, `d3.axisLeft`, and `d3.axisBottom` from D3, renders as SVG, and applies styling through an external CSS file for font sizes and colors.