mdb-ui-kit/scss/_popover.scss

.popover, .tooltip-inner {
  line-height: 1em;
  color: $mdb-popover-color;
  background: $mdb-popover-background;
  border: 0;
  border-radius: $border-radius-base;
  @include shadow-z-1();
}

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

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