You can combine any freeform surfaces, e.g. rectangles with rounded corners or sections of circles from polylines, lines and arcs. You can then give these surfaces a fill pattern, for example.
1.Arrange several polylines, lines and arcs so that they form a closed border. Make sure that the ends are as flush as possible next to each other.
2.Select all of the objects that are to form the freeform surface.
3.Choose the command Format[Edit] > Connect. The selected objects are transformed into a closed polygon to which you can add a fill pattern, for instance.