wp_get_theme_preview_path()

wp_get_theme_preview_path( string $current_stylesheet = null ): string

function wp_get_theme_preview_path( $current_stylesheet = null ) {
	if ( ! current_user_can( 'switch_themes' ) ) {
		return $current_stylesheet;
	}

	$preview_stylesheet = ! empty( $_GET['wp_theme_preview'] ) ? sanitize_text_field( wp_unslash( $_GET['wp_theme_preview'] ) ) : null;
	$wp_theme           = wp_get_theme( $preview_stylesheet );
	if ( ! is_wp_error( $wp_theme->errors() ) ) {
		if ( current_filter() === 'template' ) {
			$theme_path = $wp_theme->get_template();
		} else {
			$theme_path = $wp_theme->get_stylesheet();
		}

		return sanitize_text_field( $theme_path );
	}

	return $current_stylesheet;
}