error when install x theme

Hi, I just bought x-theme and downloaded. I have the following error message and don’t know how to fix it. Can anybody help?

**Installing Theme from uploaded file:
Unpacking the package…

Installing the theme…

The package could not be installed. The theme is missing the style.css stylesheet.

Theme installation failed.



Make sure you select the “Installable WordPress file only” option. If you select “All files &
you can check this helpful article stylesheet error