I did it. With help of some forum members I finally completed that app.
The building process was very funny and learned a lot.
This is the result: https://codepen.io/GeraltDieSocke/full/yzJrBg/
I just have a default white background. And just 3 backgrounds that changes when the status is rain, sunny or thunderstorm :D.
The weather icons however I have almost 30 or so implemented.
I have it from this site: http://erikflowers.github.io/weather-icons/
Please tell me what I did good and what I did badly. Any feedback is highly appreciated.
Have a nice day.