In the supplied subtheme, drupal8_w3css_subtheme, there are two spelling errors in the README.txt files
Each readme file has this line:
Drual8 W3CSS Sub-theme is a start up theme for your customization.
The should read:
Drupal8 W3CSS Subtheme is a start up theme for your customization.
Just download the theme
See attached patch
Fixed
2.0
Code
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