The common issue occur when installing a WordPress theme is “ The package could not be installed. The theme is missing the style.css stylesheet”. It make installing process can not be completed.
When you download theme file from Themeforest, you will have 2 options:
Option 1: Download Wordpress file only.
Option 2: Download full package (full zip folder). You will need to extract and locate the installable Wordpress file to upload when you install the theme.
Make sure that you are uploading only the installable theme which is called NameOfTheme.zip. If you upload all these file, you will get an error.
Upload the installable WordPress file admin area
Step 1: Login to your WordPress admin dashboard.
Step 2: Navigate Appearance >> Theme
Step 3: Click on Add New >> Upload
Step 4: Browse and select theme Zip file to Upload
Upload via FTP
Step 1: Unzip file package
Step 2: Connect to your FTP server and navigate to the folder where your WP is installed.
Step 3: Go to wp-content/theme/ and upload theme folder ( the path will look like this wp-content/themes/tm-nameoftheme)
Step 4: Open WP admin panel and go Appearance >> Themes on admin sidebar. Active Brook.
Note: Please make sure that file style.css include in theme file. To check it, you can open theme file and look for it.