The specific steps are as follows:

Step 1: Draw a square with the rectangle tool;

Step 2: Rotate the square by 45 degrees;

Step 3: Use the direct selection tool (shortcut key A) to select the top anchor point and delete it;

Step 4: Enlarge the strokes and change the endpoints into rounded corners, as shown in the figure;

Step 5: Use the direct selection tool (shortcut key A) to select the above two endpoints and make them smooth as shown in the figure;

Step 6: Make two copies of the finished graphics and adjust the size. The outermost figure and the middle almost overlap, and the filling color is from light to dark;

Step 7: Select three graphics, and then mix them with the mixing tool CTRL+ALT+B to select a smooth color;