0
	 */
	private function combine_rules_selectors() {
		// Build an array of selectors along with the JSON-ified styles to make comparisons easier.
		$selectors_json = array();
		foreach ( $this->css_rules as $rule ) {
			$declarations        = $rule->get_declarations()->get_declarations();
			$declaration_options = $rule->get_declarations()->get_declaration_options();
			ksort( $declarations );
			// Declaration options are keyed by property and are part of the rule identity.
			ksort( $declaration_options );
			foreach ( $declaration_options as $property => $options ) {
				if ( is_array( $options ) ) {
					ksort( $options );
					$declaration_options[ $property ] = $options;
				}
			}
			$selectors_json[ $rule->get_selector() ] = wp_json_encode(
				array(
					'declarations'        => $declarations,
					'declaration_options' => $declaration_options,
				)
			);
		}

		// Combine selectors that have the same styles.
		foreach ( $selectors_json as $selector => $json ) {
			// Get selectors that use the same styles.
			$duplicates = array_keys( $selectors_json, $json, true );
			// Skip if there are no duplicates.
			if ( 1 >= count( $duplicates ) ) {
				continue;
			}

			$declarations = $this->css_rules[ $selector ]->get_declarations();

			foreach ( $duplicates as $key ) {
				// Unset the duplicates from the $selectors_json array to avoid looping through them as well.
				unset( $selectors_json[ $key ] );
				// Remove the rules from the rules collection.
				unset( $this->css_rules[ $key ] );
			}
			// Create a new rule with the combined selectors.
			$duplicate_selectors                     = implode( ',', $duplicates );
			$this->css_rules[ $duplicate_selectors ] = new WP_Style_Engine_CSS_Rule( $duplicate_selectors, $declarations );
		}
	}
}
ebab-case.
			$font_face = static::to_kebab_case( $font_face );

			$converted_font_faces[] = $font_face;
		}

		return $converted_font_faces;
	}

	/**
	 * Converts each 'file:./' placeholder into a URI to the font file in the theme.
	 *
	 * The 'file:./' is specified in the theme's `theme.json` as a placeholder to be
	 * replaced with the URI to the font file's location in the theme. When a "src"
	 * beings with this placeholder, it is replaced, converting the src into a URI.
	 *
	 * @since 6.4.0
	 *
	 * @param array $src An array of font file sources to process.
	 * @return array An array of font file src URI(s).
	 */
	private static function to_theme_file_uri( array $src ) {
		$placeholder = 'file:./';

		foreach ( $src as $src_key => $src_url ) {
			// Skip if the src doesn't start with the placeholder, as there's nothing to replace.
			if ( ! str_starts_with( $src_url, $placeholder ) ) {
				continue;
			}

			$src_file        = str_replace( $placeholder, '', $src_url );
			$src[ $src_key ] = get_theme_file_uri( $src_file );
		}

		return $src;
	}

	/**
	 * Converts all first dimension keys into kebab-case.
	 *
	 * @since 6.4.0
	 *
	 * @param array $data The array to process.
	 * @return array Data with first dimension keys converted into kebab-case.
	 */
	private static function to_kebab_case( array $data ) {
		foreach ( $data as $key => $value ) {
			$kebab_case          = _wp_to_kebab_case( $key );
			$data[ $kebab_case ] = $value;
			if ( $kebab_case !== $key ) {
				unset( $data[ $key ] );
			}
		}

		return $data;
	}
}