Actually @anlino & @vitaliikolisnyk
Since this theme has the admin menu item for cuntomizer, no custom CSS plugin is needed. You can use Additional CSS in the customizer.
Even with block themes that remove that menu item, customizer still exists and works because most themes require it.
/wp-admin/customize.php
Likewise with /nav-menus.php and /widgets.php
They all come in handy with block themes. I find it easier to build a menu the old fashioned way. Some plugins add their own sidebar with “legacy” widgets and /widgets.php is the only place to work with those.
@vitaliikolisnyk
greenshift plugin has a special button with cookie and a tutorial on their site on how to use it to make a dark/light mode switch.
background/foreground variable gets swapped but other colors can be dealt with in the same manner, even those that are not var.