A common issue for users new to WordPress is seeing the "The package could not be installed. The theme is missing the style.css stylesheet" error when trying to upload a theme. This message doesn't mean your theme is broken. It usually occurs because you uploaded the wrong file.

Most likely, instead of uploading the "Installable WordPress file only" you may have uploaded the "All files & documentation" package. This package contains extra files like documentation, which WordPress doesn't recognize as a theme.

For more information about this issue, you can visit this guide:

https://help.market.envato.com/hc/en-us/articles/202821510-Theme-is-missing-the-style-css-stylesheet-error