hp/js/editor.js

wp.domReady( () => {
  wp.blocks.unregisterBlockStyle( 'core/button', ['default', 'outline', 'squared', 'fill'] );
  wp.blocks.registerBlockStyle( 'core/button', [
      {
        name: 'bootstrap-outline-secondary',
        label: 'Purple Outline',
        isDefault: true
      },
      {
        name: 'bootstrap-secondary',
        label: 'Purple Solid'
      },
      {
        name: 'bootstrap-outline-primary',
        label: 'Green Outline'
      },
      {
        name: 'bootstrap-primary',
        label: 'Green Solid'
      }
    ]
  );
});