There are a few things you can do to create a custom fill in Illustrator. First, open the File menu and select New. Then, enter a name for your fill in and click OK. Next, open the Stroke panel and select a color. Then, use the Line tool to draw a line across your fill in. Be sure to use a straight line and make sure the pen is at an angle so that it curves slightly towards the edge of your fill in. Next, use the Polygon tool to create shapes around your line. You can choose to have these shapes be circles, squares, or triangles. Finally, use the Path tool to draw lines between each shape and then press OK.
