doc/dev/plugins/problems/scss/_popovers.scss

// Popovers
.popover {
  display: inline-block;
  position: relative;

  .popover-container {
    left: 50%;
    opacity: 0;
    padding: $layout-spacing;
    position: absolute;
    top: 0;
    transform: translate(-50%, -50%) scale(0);
    transition: transform .2s ease;
    width: $control-width-sm;
    z-index: $zindex-3;
  }

  *:focus + .popover-container,
  &:hover .popover-container {
    display: block;
    opacity: 1;
    transform: translate(-50%, -100%);
  }

  &.popover-right {
    .popover-container {
      left: 100%;
      top: 50%;
    }

    *:focus + .popover-container,
    &:hover .popover-container {
      transform: translate(0, -50%);
    }
  }

  &.popover-bottom {
    .popover-container {
      left: 50%;
      top: 100%;
    }

    *:focus + .popover-container,
    &:hover .popover-container {
      transform: translate(-50%, 0);
    }
  }

  &.popover-left {
    .popover-container {
      left: 0;
      top: 50%;
    }

    *:focus + .popover-container,
    &:hover .popover-container {
      transform: translate(-100%, -50%);
    }
  }

  .card {
    @include shadow-variant(.2rem);
    border: 0;
  }
}