Design a digital post-it / sitcky note quickly with photoshop.
Create new layer and name it as “sticky note”. Select the Rectangular tool and set the foreground to yellow like #fcf185 and drag in the workspace while holding the Shift key in your keyboard to constrain a proportion. Then press ALT+Backspace to fill it. Do not deselect yet.
Create again a new layer and name it as “paste”. This will serve as the paste part of the sticky note. With the paste layer selected, drag a part on the selection to be subtracted.