index.html

  <!-- 主导航栏 -->
  <nav>
    <div class="nav-common">
      <div class="nav-items">1</div>
      <div class="nav-items">1</div>
      <div class="nav-items">1</div>
    </div>
    <div class="nav-common">2</div>
    <div class="nav-common">3</div>
  </nav>

index.css

/* 主导航栏 */
nav {
  border-radius: 10px;
  margin: 3px 5px 3px;
}

nav .nav-common {
  display: flex;
  height: 88px;
  background-color: blue;
}


nav .nav-common:nth-child(2) {
  margin: 3px 0;
}

nav .nav-common .nav-items {
  flex: 1px;
}

nav .nav-common .nav-items:nth-child(-n+2) {
  border-right: 1px solid #fff;
}