<div class="block">
  <code>border-bottom: 10px solid #666;</code>
</div>
.block {
  width: 500px;
  height: 250px;
  background-color: #eee;
  border-bottom: 10px solid #666;
  text-align: center;
  font-size: 19px;
  padding-top: 18%;
  box-sizing: border-box;
}

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External JavaScript

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