protected function process_blocks_custom_css( $css, $selector ) {
    $processed_css = '';

    // Split CSS nested rules.
    $parts = explode( '&', $css );
    foreach ( $parts as $part ) {
      $is_root_css = ( ! str_contains( $part, '{' ) );
      if ( $is_root_css ) {
        // If the part doesn't contain braces, it applies to the root level.
        $processed_css .= trim( $selector ) . '{' . trim( $part ) . '}';
      } else {
        // If the part contains braces, it's a nested CSS rule.
        $part = explode( '{', str_replace( '}', '', $part ) );
        if ( count( $part ) !== 2 ) {
          continue;
        }
        $nested_selector = $part[0];
        $css_value       = $part[1];
        $part_selector   = str_starts_with( $nested_selector, ' ' )
          ? static::scope_selector( $selector, $nested_selector )
          : static::append_to_selector( $selector, $nested_selector );
        $processed_css  .= $part_selector . '{' . trim( $css_value ) . '}';
      }
    }
    return $processed_css;
  }