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. 😃