<h2 class="title">這是一個標題</h2>
.title {
  position: relative;
  padding-bottom: 10px;
  text-align: center;
}

.title::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 0;
  width: 100%;
  height: 3px;
  border-bottom: 2px dashed #000; /* 虛線樣式的底線 */
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.