Missing style sheet error when installing the theme?
If you receive this error, it means you've uploaded wrong zip file to your WordPress dashboard.
You've downloaded All files & documentation, like in screenshot :
Please extract that zip file and inside that folder you can see theme file, documentation, license, and other files. Please upload theme file, that's mostly named as theme-name.zip [eg : juster.zip]
That's the exact file to upload in your : Appearance > Themes
This might be helpful :
Common WordPress Installation Issues