ホバー
CSS

Grow Underline

ホバーで中央から左右に広がるアンダーライン。

HTML
<nav class="grow-nav">
  <a href="javascript:void(0)">Home</a>
  <a href="javascript:void(0)">Blog</a>
  <a href="javascript:void(0)">About</a>
</nav>
CSS
.grow-nav {
  display: flex;
  gap: 1.5rem;
}
.grow-nav a {
  position: relative;
  font-size: 14px;
  font-weight: 500;
  color: #666;
  text-decoration: none;
  padding-bottom: 4px;
  transition: color .2s;
}
.grow-nav a::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 50%;
  width: 0;
  height: 1.5px;
  background: #1a1a1a;
  transition: all .3s cubic-bezier(.4,0,.2,1);
}
.grow-nav a:hover { color: #1a1a1a; }
.grow-nav a:hover::after {
  left: 0;
  width: 100%;
}