A line chart displays the percentage of positive PCR tests per day for a selected Italian region, using a dropdown menu to switch between them. The data comes from the Italian government's COVID-19 regional dataset, filtered to the last 90 days. Built with React and D3 v6, the SVG visualization uses `scaleTime` for the x-axis, `scaleLinear` for the y-axis, and `line` from d3 to draw the path, with circles and tooltips for each data point.