Cloning the Base theme bartik, seven, and stark in Drupal 8 I tried copying the seven theme from /core/theme into my own /theme folder. I renamed all the files that starts with seven to sevenx and also renamed the seven_ functions to sevenx_ and it still not showing up on the theme pages. 


What else do I need to change to make drupal 8 see this new cloned theme?
Is there a quick tool to get this done without having me to rename everything?
A few things that could have been missed -

Cache clear,
Changing the name of the theme in .info.yml of the new theme,
Not putting the base theme in the .info.yml.

If none of those work, this is a pretty good guide. https://www.drupal.org/theme-guide/8/creating-a-sub-theme