The border panel lets you have control over the different aspects of the border.
Use the color picker to adjust the border color.
Adjust individually or simultaneously the 4 sides of the border width. When the lock icon is purple, all 4 sides are changed at the same time.
Border radius lets you have rounded corners. Set to a high value to have the layer look like a circle, given that its width equals its height.
Adjust individually or simultaneously the radius of the 4 corners. When the lock icon is purple, all 4 corners are changed at the same time.