下線付き見出し

<h2 class="heading-framed">注意事項</h2>

.heading-framed {
  position: relative;
  font-size: 18px;
  font-weight: 600;
  color: #1f2937;
  text-align: center;
  padding: 16px 12px;
  margin: 40px 0;
}

.heading-framed::before,
.heading-framed::after {
  content: '';
  position: absolute;
  left: 10%;
  right: 10%;
  height: 1px;
  background: #9ca3af;
}

.heading-framed::before {
  top: 8px;
}

.heading-framed::after {
  bottom: 8px;
}