// theme.json Spacing-Scale
add_filter(
  'gpx_spacing_scale',
  function( $scale ) {
    $scale['steps'] = 7;
    $scale['unit']  = 'rem';
    return $scale;
  }
);

// Custom Block Styles
add_filter(
  'gpx_block_styles',
  function( $styles ) {
    $styles[] = [
      'block' => 'core/button',
      'name'  => 'outline',
      'label' => 'Outline',
    ];
    return $styles;
  }
);

// Typography Presets
add_filter(
  'gpx_font_families',
  function( $fonts ) {
    $fonts['mono'] = 'Fira Code';
    return $fonts;
  }
);

functions.php / gpx_filters