Problem with uploading style.css

I just downloaded wordpress and was uploading a theme (using filezilla) to the themes folder. All of them uploaded except style.css.
This error was shown:

553 Filetype not allowed. File style.css won’t be saved.

I even tried other themes to check if the first one was corrupted, but it turned out the same for all of them.
I even tried renaming it.
style.css just won’t upload.