How to install Bulma theme

1. Install Bulma theme as usual in Drupal 8 (see Drupal 8 docs).
2. Create your own subtheme with drush command (please note this no longer works with Drush 9 or later, see #2960328: Update Bulma Drush commands to Drush 9)
   

   drush bulma "my sub-theme"

   or step-by-step, see documentation

3. Customize Sass (SCSS files) inside your sub-theme which you have created. (Not inside base theme)
4. By default, Bulma uses a CDN. If you wish to instead use a local version, download the latest Bulma release and install it at libraries/bulma. If using a custom Bulmaswatch theme (see the theme settings), you may also download the latest Bulmaswatch release to libraries/bulmaswatch.

Additionally, check theme settings page to activate specific features.