aleksvor Yes, a friend told me about the risks.
I made sudo nautilus /usr/share/themes and I never should do this. So, I deleted immediately the themes I pasted. I hope I did not make something wrong to my computer.
So, I went to /home/alan and I clicked on Ctrl + H. I saw .local folder. Then, I went to share folder and I created themes folder. I pasted my theme. And voilà . It worked. 😃