The main difference between theming of Drupal 7 & Drupal 8 is theme engine. In Drupal 7 supports PHPTemplate and Drupal 8 leverages Twig engine
Step 1: Create .info file
An Important part of Drupal theme or module is .info file. Through this file drupal will understand whether it is theme or module.
In Drupal 7 it was .info but in D8 it changes to .info.yml (called as yaml). So to create a theme, first create a folder and name it after the theme. In this case let’s say theme name is “Invezza”, So create a folder of name invezza. Notice that all letters are in small. Now in this folder create a file and save it as invezza.info.yml. This is our info file. The rest is same as Drupal 7 .info file Read More