papercss/src/components/_popovers.scss

// Core popovers
[popover-top],
[popover-right],
[popover-bottom],
[popover-left] {
  margin: 24px;
  position: relative;

  // Popover hover trigger
  &:hover {
    &::after {
      opacity: 1;
      transition: opacity 0.2s ease-out;
    }
  }

  // Creating popover::after element
  &::after {
    @include border-style();
    @include transition(opacity);
    @include color('background-color', 'light-dark');
    @include color('border-color', 'light-dark');
    @include color('color', 'primary-inverse');
    border-style: solid;
    border-width: 2px;
    font-size: 0.7em;
    left: 50%;
    min-width: 80px;
    opacity: 0;
    padding: 4px 2px;
    position: absolute;
    text-align: center;
    top: -6px;
    transform: translateX(-50%) translateY(-100%);
  }
}

// Popover positioning: left, right, top, bottom
[popover-left] {
  &::before {
    left: 0;
    margin-left: -12px;
    top: 50%;
    transform: translateY(-50%) rotate(-90deg);
  }

  &::after {
    content: attr(popover-left);
    left: 0;
    margin-left: -8px;
    top: 50%;
    transform: translateX(-100%) translateY(-50%);
  }
}

[popover-right] {
  &::before {
    left: 100%;
    margin-left: 1px;
    top: 50%;
    transform: translatey(-50%) rotate(90deg);
  }

  &::after {
    content: attr(popover-right);
    left: 100%;
    margin-left: 8px;
    top: 50%;
    transform: translateX(0%) translateY(-50%);
  }
}

[popover-top] {
  &::before {
    left: 50%;
  }

  &::after {
    content: attr(popover-top);
    left: 50%;
  }
}

[popover-bottom] {
  &::before {
    margin-top: 8px;
    top: 100%;
    transform: translateX(-50%) translatey(-100%) rotate(-180deg);
  }

  &::after {
    content: attr(popover-bottom);
    margin-top: 8px;
    top: 100%;
    transform: translateX(-50%) translateY(0%);
  }
}