<div class="balloon-down">
  <p>下向きの吹き出し</p>
</div>
.balloon-down {
  position: relative;
  display: inline-block;
  margin: .5em 0;
  padding: 0 10px;
  min-width: 120px;
  max-width: 100%;
  color: #333;
  font-size: 16px;
  background: #FFF;
  border: solid 3px #555;
  box-sizing: border-box;
}

.balloon-down:before {
  content: "";
  position: absolute;
  bottom: -24px;
  left: 50%;
  margin-left: -15px;
  border: 12px solid transparent;
  border-top: 12px solid #FFF;
  z-index: 2;
}

.balloon-down:after {
  content: "";
  position: absolute;
  bottom: -30px;
  left: 50%;
  margin-left: -17px;
  border: 14px solid transparent;
  border-top: 14px solid #555;
  z-index: 1;
}

External CSS

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External JavaScript

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