Changing the color of some divs to the same as body.custom-background?

Question

WordPress

I change the background color in the theme using wp-admin/customize.php in the WP console
. After that, the body has an additional class body.custom-background.
How can I now apply this color to some more divs in this theme?

I tried to add this class via

const element = document.querySelector('.site-title');
element.classList.add('custom-background');

but it doesn't work like that

Answer 1

Question - how?

... apply this color to some more divs in this theme?

like this for example

add_action('wp_head','div_style');
if(!function_exists('div_style')){function div_style(){?>
<style id="div_style" type="text/css">
  .div_style{background-color:#<?php echo get_theme_mod('background_color');?>;}
</style>
<?php }}

...............или...............

add_action('get_footer','div_style');
if(!function_exists('div_style')){function div_style(){?>
<style id="div_style" type="text/css">
  .div_style{background-color:#<?php echo get_theme_mod('background_color');?>;}
</style>
<?php }}

разметка: