How to correct event site background
Go to Setup
Feature Settings
Digital Experiences
All Sites
On the National Events click on Builder -> This will open the Builder of the community.
On the community builder you need to select LT Event
Once you select it you need to go to click on Theme -> Click on the top right left of the arrow
Select edit css
Add this to the popup-
.widgets-events.pfm-event-page-body.LTEEventPage{
background-color: #FFFFFF !important;
}