A common issue that can occur with users new to installing WordPress themes is a “Broken theme and/or stylesheets missing” error message being displayed when trying to upload or activate the theme.
This error message does not mean that the item is not working, it simply means it has been uploaded incorrectly.
After downloading the Specular theme folder from your Envato account, you should unzip it. Inside the main folder, there are located several folders. The specular folder, documentation, Licensing, sliders_dummy_data and specular-child folder.
The specular folder is the one you need. Select it and upload into your wp-content\themes folder via ftp. Or you can zip it and import it from your WordPress dashboard (Appearance > Themes > Add new).
Or you can download ONLY the installable file.