The "Filled Rectangle Tool" draws the filled outline rectangles. The filled type fill the rectangle with the
background color.

To draw a filled outline rectangles, click on the tool, then click a point on the icon where you want one corner
to be, then drag diagonally and release the mouse where you want the opposite corner to be.

Example:

Here's a composition creating using only the filleg rectangles with outline.

Hotkey for using this Tool is CTRL + F.