1. The category axis line indicates the line of the category axis(x-axis), once the user clicks on the category axis line option, you can enable the category axis line by clicking on the toggle button which will open the control options as shown in the below figure.

2. The Border width is used to set the width of line.

3. Border opacity is used to set the visibility of the category line in chart.

4. Color controls the color of the category line, from color user can also control the opacity and choose color from color code.