ngbTooltop add a custom class

 https://ng-bootstrap.github.io/#/components/tooltip/examples

https://stackoverflow.com/questions/70569817/apply-custom-styles-to-ngbtooltip-in-angular

<button type="button" ngbTooltip="Upload new document" tooltipClass="my-custom-class">
  <img src="plus_button.jpg">
</button>

.my-custom-class .tooltip-inner {
   background-color: lightblue;
}

.my-custom-class .arrow::before {
   border-top-color: lightblue;
}