mdb-ui-kit/sass/_popups.scss

.popover, .tooltip-inner {
  color: $popover-color;
  line-height: 1em;
  background: $popover-background;
  border: none;
  border-radius: $material-border-radius;
  @extend .shadow-z-1;
}

.tooltip, .tooltip.in {
  opacity: 1;
}

.popover, .tooltip {
  .arrow, .tooltip-arrow {
    display: none;
  }
}