function block_core_gallery_render( $attributes, $content ) {
  $gap = _wp_array_get( $attributes, array( 'style', 'spacing', 'blockGap' ) );
  // Skip if gap value contains unsupported characters.
  // Regex for CSS value borrowed from `safecss_filter_attr`, and used here
  // because we only want to match against the value, not the CSS attribute.
  if ( is_array( $gap ) ) {
    foreach ( $gap as $key => $value ) {
      $gap[ $key ] = $value && preg_match( '%[\\\(&=}]|/\*%', $value ) ? null : $value;
    }
  } else {
    $gap = $gap && preg_match( '%[\\\(&=}]|/\*%', $gap ) ? null : $gap;
  }

  $class   = wp_unique_id( 'wp-block-gallery-' );
  $content = preg_replace(
    '/' . preg_quote( 'class="', '/' ) . '/',
    'class="' . $class . ' ',
    $content,
    1
  );

  // --gallery-block--gutter-size is deprecated. --wp--style--gallery-gap-default should be used by themes that want to set a default
  // gap on the gallery.
  $fallback_gap = 'var( --wp--style--gallery-gap-default, var( --gallery-block--gutter-size, var( --wp--style--block-gap, 0.5em ) ) )';
  $gap_value    = $gap ? $gap : $fallback_gap;
  $gap_column   = $gap_value;

  if ( is_array( $gap_value ) ) {
    $gap_row    = isset( $gap_value['top'] ) ? $gap_value['top'] : $fallback_gap;
    $gap_column = isset( $gap_value['left'] ) ? $gap_value['left'] : $fallback_gap;
    $gap_value  = $gap_row === $gap_column ? $gap_row : $gap_row . ' ' . $gap_column;
  }

  // Set the CSS variable to the column value, and the `gap` property to the combined gap value.
  $style = '.' . $class . '{ --wp--style--unstable-gallery-gap: ' . $gap_column . '; gap: ' . $gap_value . '}';

  // Ideally styles should be loaded in the head, but blocks may be parsed
  // after that, so loading in the footer for now.
  // See https://core.trac.wordpress.org/ticket/53494.
  add_action(
    'wp_footer',
    function () use ( $style ) {
      echo '<style> ' . $style . '</style>';
    },
    11
  );
  return $content;
}