Last couple of hours I was trying to figure out how can I copy some feature in that web site:
How can I add that animated icon which can change from " plus " to " minus " in that widget?
P\S Widget doesn't allow me to paste an icon to the top tabs of the widget.
You need two images - plus and minus. In the standard panel state, use the "plus" (fill > select an image, scale to FIt, position on the right), in the active state of the panel use "minus" (fill > select an image, scale to FIt, position on the right).
Thanks for your answer. But what if I would like to keep some space between edge of the widget and an icon as the example of the website which mentioned before in that discussion.
Make in Photoshop image with your desired indented
By the way, if somebody wants to add "plus" or "Minus" and don't want to loose quality, you can do that in Illustrator as well.