Give a block a class based on ID in modern Drupal 8 9 10

The ID used for the actual ID attribute tends to be sorta idiosyncratic and ugly. The Plugin ID tends to make a better source for a place to hang markup.

plugin_id: page_title_block

base_plugin_id is same

no derivative plugin

Following the same pattern: system_main_block with a block originalID of greenhouse_vhfa_system_main

system_messages_block " menu " " branding "

system_menu_block:menu-header-menu

$variables[“plugin_id”] = “block_content:80cded59-9651-5dae-bfeb-78a1930c76”