How do you add a border radius in Illustrator?

You can add a border radius (round corners) to shapes in Adobe Illustrator using the Live Corners feature.

Here's how:

1. Select the Direct Selection Tool (A): This tool allows you to select individual corners of a shape.
2. Select the Shape: Click on the shape you want to round the corners of.
3. Identify the Live Corners Widgets: Small circles will appear near each corner of the shape. These are the Live Corners widgets.
4. Drag the Live Corners Widgets: Click and drag one of the Live Corners widgets towards the center of the shape. All corners will begin to round uniformly.
5. Rounding Specific Corners: If you only want to round specific corners, use the Direct Selection Tool (A) to click directly on the corner you want to adjust. The other corner widgets will disappear, leaving only the one you selected active. Now, drag the active widget to adjust just that corner.
6. Adjusting Radius Value: You can also double-click on a Live Corners widget to open the Corners dialog box, where you can enter a precise radius value for each corner.

By using the Live Corners feature, you can easily and precisely control the rounding of corners in your Illustrator designs.