How to create custom widgets?

[Mimoid]

Hello. I want to do nicer application with professional design, not using only basic widgets and elements.
Have you tutorials or advices how can i do this?
Example : https://www.youtube.com/watch?v=I6NbNTStEv0 (These black elements e.g "Add audio" and others)

[mrjj]

Hi
well you can change most looks using style sheets.
http://doc.qt.io/qt-5/stylesheet-examples.html

there is also QML which is aimed at the mobile world.

http://doc.qt.io/qt-5/qtqml-index.html

Also, to make nice designs, you must be good with colors etc.
There are many sites devoted to UI creation and design.