The control buttons in crm pop ups are all X's

The icons in crm-pop-up title bars in backdrop all display as X's see screenshot below:

They should display as whatever font awesome icon is assigned to them usually something like print, minimize, maximize or close see screenshot below:

Reproducible on bmaster.demo.civicrm.org.

added regression label

Opened a pr: https://github.com/civicrm/civicrm-core/pull/24930

added has-pull-request label

mentioned in commit core@358ce143

mentioned in commit core@bc0b4f70

changed milestone to %5.55.2

PR port open but already merged to 5.56 rc https://github.com/civicrm/civicrm-core/pull/24936

closed

mentioned in commit core@84d5e8cd

mentioned in commit core@5666c027