How to format chart and plot area
All charts in Excel have a chart area, which encloses all elements of the chart. The easiest way to grab the chart area is to click just below the top edge of the chart. Once the chart area is selected, you’re free to make a variety of formatting changes. To change the line around a chart, use the controls in the Border area. You’ll find controls for color, thickness, and many other line attributes, including rounded corners....