I got error message “stylesheets missing”

I got error message “stylesheets missing” when I try to installing the theme.
What shuld i do?
If I install with "Using Envato WordPress Toolkit - preferred method" where shall I put inn the API?
I dont anderstand where to "Install and activate the toolkit plugin. A new menu item, “Envato Toolkit,” will appear in "
2. Install Envato WordPress Toolkit Plugin

Install and activate the toolkit plugin. A new menu item, “Envato Toolkit,” will appear in the admin sidebar. Click on the sidebar link and enter your marketplace username and secret API key. Click “Save Settings.”