<div class="l-content">
  <div class="l-content__section">
	  <h2 class="c-title">１２３４５６７８９１０１２３４５６７８９１０</h2>
  </div>
  <div class="l-content__section">
    <h2 class="c-title">１２３４５６７８９１０</h2>
  </div>
  <div class="l-content__section">
  	<h2 class="c-title">１２</h2>
  </div>
</div>

* {
  margin: 0;
  padding: 0;
}
body {
  padding: 2%;
  box-sizing: border-box;
}
.l-content {
	display: grid;
  gap: 16px 0;
}
.c-title {
  display: inline-block;
  white-space: nowrap;
  position: relative;
}
.c-title::after {
  display: block;
  content: "";
  width: 100%;
  height: 1px;
  background-color: #000;
  transform: scaleX(0);
  transform-origin: center left;
  animation: bar 4s linear forwards;
  position: absolute;
  bottom: 1px;
  left: 0;
}
@keyframes bar {
  0%   { transform: scaleX(0); }
  100% { transform: scaleX(1); }
}