Two draggable panes demonstrate interactive split-pane resizing using D3 v5 and React. The `d3.drag` API handles pointer events on a central divider, updating pane widths via the `setOffset` function, which recalculates each pane’s style width in pixels. Starting with the left pane at one-third of the viewport width, the layout responds live to dragging, with the container’s width read from its computed style. The example employs HTML/CSS for structure and styling, with D3’s `select`, `selectAll`, and `event` utilities coordinating the interaction.