<ul class="list">
  <li class="item">
    <div class="block" data-direction="upward">upward</div>
  </li>
  <li class="item">
    <div class="block" data-direction="rightward">rightward</div>
  </li>
  <li class="item">
    <div class="block" data-direction="downward">downward</div>
  </li>
  <li class="item">
    <div class="block" data-direction="leftward">leftward</div>
  </li>
  <li class="item">
    <div class="block" data-direction="upper-left">upper-left</div>
  </li>
  <li class="item">
    <div class="block" data-direction="upper-right">upper-right</div>
  </li>
  <li class="item">
    <div class="block" data-direction="lower-right">lower-right</div>
  </li>
  <li class="item">
    <div class="block" data-direction="lower-left">lower-left</div>
  </li>
</ul>

@mixin triangle($direction, $width, $height, $color: currentColor) {
  @if not index(upward rightward downward leftward upper-left upper-right lower-right lower-left, $direction) {
    @error 'triangle()の方向は"upward","rightward","downward","leftward","upper-left","upper-right","lower-right","lower-left"から指定してください';
  }

  border-style: solid;
  height: 0;
  width: 0;

  @if $direction == upward {
    border-color: transparent transparent $color transparent;
    border-width: 0 ($width / 2) $height ($width / 2);
  }

  @if $direction == rightward {
    border-color: transparent transparent transparent $color;
    border-width: ($height / 2) 0 ($height / 2) $width;
  }

  @if $direction == downward {
    border-color: $color transparent transparent transparent;
    border-width: $height ($width / 2) 0 ($width / 2);
  }

  @if $direction == leftward {
    border-color: transparent $color transparent transparent;
    border-width: ($height / 2) $width ($height / 2) 0;
  }

  @if $direction == upper-left {
    border-color: $color transparent transparent transparent;
    border-width: $height $height 0 0;
  }

  @if $direction == upper-right {
    border-color: transparent $color transparent transparent;
    border-width: 0 $height $height 0;
  }

  @if $direction == lower-right {
    border-color: transparent transparent $color transparent;
    border-width: 0 0 $height $height;
  }

  @if $direction == lower-left {
    border-color: transparent transparent transparent $color;
    border-width: $height 0 0 $height;
  }
}

html {
  box-sizing: border-box;
}

*,
*::before,
*::after {
  box-sizing: inherit;
}

body {
  background: #f7f7f7;
  color: #3a3a3a;
  font-family: 'Open Sans', 'Helvetica Neue', 'Segoe UI', 'Hiragino Sans', 'Hiragino Kaku Gothic ProN', Meiryo, sans-serif;
  font-size: 1em;
  line-height: 1.5;
  padding: 5%;
}

.list {
  display: grid;
  gap: 8px;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  margin: auto;
  max-width: 1200px;
}

.item {
  display: grid;
  padding: 32px;
  place-items: center;
}

.block {
  background-color: #cd5c5c;
  border-radius: 4px;
  box-shadow: 0 10px 12px -8px rgba(0, 0, 0, 0.35);
  color: #f7f7f7;
  font-size: 1rem;
  line-height: 1.5;
  min-width: 196px;
  padding: 1.2em 1.5em;
  position: relative;
  text-align: center;

  &::before {
    content: '';
    display: inline-block;
    position: absolute;
  }
}

[data-direction='upward'] {
  &::before {
    @include triangle(upward, 20px, 15px, #cd5c5c);

    bottom: 100%;
    left: calc(50% - 10px);
  }
}

[data-direction='rightward'] {
  &::before {
    @include triangle(rightward, 15px, 20px, #cd5c5c);

    left: 100%;
    top: calc(50% - 10px);
  }
}

[data-direction='downward'] {
  &::before {
    @include triangle(downward, 20px, 15px, #cd5c5c);

    left: calc(50% - 10px);
    top: 100%;
  }
}

[data-direction='leftward'] {
  &::before {
    @include triangle(leftward, 15px, 20px, #cd5c5c);

    right: 100%;
    top: calc(50% - 10px);
  }
}

[data-direction='upper-left'] {
  &::before {
    @include triangle(upper-left, 12px, 12px);

    left: 6px;
    top: 6px;
  }
}

[data-direction='upper-right'] {
  &::before {
    @include triangle(upper-right, 12px, 12px);

    right: 6px;
    top: 6px;
  }
}

[data-direction='lower-right'] {
  &::before {
    @include triangle(lower-right, 12px, 12px);

    bottom: 6px;
    right: 6px;
  }
}

[data-direction='lower-left'] {
  &::before {
    @include triangle(lower-left, 12px, 12px);

    bottom: 6px;
    left: 6px;
  }
}