twbs--bootstrap/scss/_popover.scss

.popover {
  position: absolute;
  top: 0;
  left: 0;
  z-index: $zindex-popover;
  display: block;
  max-width: $popover-max-width;
  padding: 1px;
  // Our parent element can be arbitrary since tooltips are by default inserted as a sibling of their target element.
  // So reset our font and text properties to avoid inheriting weird values.
  @include reset-text();
  font-size: $font-size-sm;
  // Allow breaking very long words so they don't overflow the popover's bounds
  word-wrap: break-word;
  background-color: $popover-bg;
  background-clip: padding-box;
  border: $popover-border-width solid $popover-border-color;
  @include border-radius($border-radius-lg);
  @include box-shadow($popover-box-shadow);


  // Popover directions

  &.popover-top,
  &.bs-tether-element-attached-bottom {
    margin-top: -$popover-arrow-width;

    .popover-arrow {
      bottom: -$popover-arrow-outer-width;
      left: 50%;
      margin-left: -$popover-arrow-outer-width;
      border-top-color: $popover-arrow-outer-color;
      border-bottom-width: 0;
      &::after {
        bottom: 1px;
        margin-left: -$popover-arrow-width;
        content: "";
        border-top-color: $popover-arrow-color;
        border-bottom-width: 0;
      }
    }
  }

  &.popover-right,
  &.bs-tether-element-attached-left {
    margin-left: $popover-arrow-width;

    .popover-arrow {
      top: 50%;
      left: -$popover-arrow-outer-width;
      margin-top: -$popover-arrow-outer-width;
      border-right-color: $popover-arrow-outer-color;
      border-left-width: 0;
      &::after {
        bottom: -$popover-arrow-width;
        left: 1px;
        content: "";
        border-right-color: $popover-arrow-color;
        border-left-width: 0;
      }
    }
  }

  &.popover-bottom,
  &.bs-tether-element-attached-top {
    margin-top: $popover-arrow-width;

    .popover-arrow {
      top: -$popover-arrow-outer-width;
      left: 50%;
      margin-left: -$popover-arrow-outer-width;
      border-top-width: 0;
      border-bottom-color: $popover-arrow-outer-color;
      &::after {
        top: 1px;
        margin-left: -$popover-arrow-width;
        content: "";
        border-top-width: 0;
        border-bottom-color: $popover-arrow-color;
      }
    }
  }

  &.popover-left,
  &.bs-tether-element-attached-right {
    margin-left: -$popover-arrow-width;

    .popover-arrow {
      top: 50%;
      right: -$popover-arrow-outer-width;
      margin-top: -$popover-arrow-outer-width;
      border-right-width: 0;
      border-left-color: $popover-arrow-outer-color;
      &::after {
        right: 1px;
        bottom: -$popover-arrow-width;
        content: "";
        border-right-width: 0;
        border-left-color: $popover-arrow-color;
      }
    }
  }
}


// Offset the popover to account for the popover arrow
.popover-title {
  padding: $popover-title-padding-y $popover-title-padding-x;
  margin: 0; // reset heading margin
  font-size: $font-size-base;
  background-color: $popover-title-bg;
  border-bottom: $popover-border-width solid darken($popover-title-bg, 5%);
  $offset-border-width: ($border-width / $font-size-root);
  @include border-radius(($border-radius-lg - $offset-border-width) ($border-radius-lg - $offset-border-width) 0 0);
}

.popover-content {
  padding: $popover-content-padding-y $popover-content-padding-x;
}


// Arrows
//
// .popover-arrow is outer, .popover-arrow::after is inner

.popover-arrow {
  &,
  &::after {
    position: absolute;
    display: block;
    width: 0;
    height: 0;
    border-color: transparent;
    border-style: solid;
  }
}
.popover-arrow {
  border-width: $popover-arrow-outer-width;
}
.popover-arrow::after {
  content: "";
  border-width: $popover-arrow-width;
}