Fatal error: Uncaught Error: Undefined constant “HEADER”

After updating to wordpress 5.7.1 I got this error and cannot activate this theme anymore.

Fatal error: Uncaught Error: Undefined constant "HEADER" in /var/www/hempoilcbdbenefits.com/html/wp-content/themes/sparkling/inc/custom-header.php:56 Stack trace: #0 /var/www/hempoilcbdbenefits.com/html/wp-includes/class-wp-hook.php(292): sparkling_header_style() #1 /var/www/hempoilcbdbenefits.com/html/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters() #2 /var/www/hempoilcbdbenefits.com/html/wp-includes/plugin.php(484): WP_Hook->do_action() #3 /var/www/hempoilcbdbenefits.com/html/wp-includes/general-template.php(3009): do_action() #4 /var/www/hempoilcbdbenefits.com/html/wp-content/themes/sparkling/header.php(30): wp_head() #5 /var/www/hempoilcbdbenefits.com/html/wp-includes/template.php(730): require_once('...') #6 /var/www/hempoilcbdbenefits.com/html/wp-includes/template.php(676): load_template() #7 /var/www/hempoilcbdbenefits.com/html/wp-includes/general-template.php(48): locate_template() #8 /var/www/hempoilcbdbenefits.com/html/wp-content/themes/sparkling/index.php(11): get_header() #9 /var/www/hempoilcbdbenefits.com/html/wp-includes/template-loader.php(106): include('...') #10 /var/www/hempoilcbdbenefits.com/html/wp-blog-header.php(19): require_once('...') #11 /var/www/hempoilcbdbenefits.com/html/index.php(17): require('...') #12 {main} thrown in /var/www/hempoilcbdbenefits.com/html/wp-content/themes/sparkling/inc/custom-header.php on line 56

This is my server configuration:

Server architecture	Linux 4.18.0-240.22.1.el8_3.x86_64 x86_64
Web server	Apache/2.4.37 (centos) OpenSSL/1.1.1g
PHP version	8.0.5 (Supports 64bit values)
PHP SAPI	fpm-fcgi
PHP max input variables	1000
PHP time limit	600
PHP memory limit	1024M
Max input time	600
Upload max filesize	1024M
PHP post max size	1024M
cURL version	7.61.1 OpenSSL/1.1.1g
Is SUHOSIN installed?	No
Is the Imagick library available?	Yes
Are pretty permalinks supported?	Yes
.htaccess rules	Custom rules have been added to your .htaccess file.

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