<header>
  <nav>
    <ul>
      <li>
        <a href ="#">
          <span class="weight">HOME</span>
          </a>
      </li>
      <li>
        <a href="#">
        <span class="weight">事業内容</span>
          </a>
        <ul class="inner-ul">
          <li><a href="#">App</a></li>
          <li><a href="#">Web</a></li>
          <li><a href="#">Design</a></li>
        </ul>
      </li>
      <li><a href="#">
        <sapn class="weight">アクセス</sapn>
         </a></li>
    </ul>
  </nav>
</header>
nav > ul {
  display: inline-block;
  position: relative;
}

nav > ul > li {
  float: left;
  position: relative;
  width:;
}

.weight {
  font-weight: 900;
  display: block;
}

li {
  padding: 1em 1em;
  list-style: none;
}

.inner-ul {
  position: absolute;
  left: -30px;
}

.textred {
  color: red;
}

.bordernone {
  text-decoration: none;
}

.textgreen {
  color: green;
}
$("li .weight").eq(0).addClass("textred");
$("li:nth-child(3) a").addClass("bordernone");
$("li .weight").eq(-1).addClass("textgreen");

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/vue/2.6.11/vue.min.js
  2. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js