You can get shading using reference lines, but they are plotted at the value not at a certain alignment like the center of the bar.
There is a lot of chart junk in there. You are labeling every point on two different axes that are visible, plus borders and grid lines. It is a good practice to not try and replicate Excel in Tableau. There is usually a better way to visualize the data.
Jeremy.twbx 1.2 MB