4. Boostrap4 元件

一、導航

1. http://bootstrap.hexschool.com/docs/4.0/components/navs/
2. 可用無序列表 ul.nav 
3. 項目 li.nav-item 
4. 連結：a.nav-link 作用中 .active 禁用：.disabled
5. 垂直導航：.nav.flex-column 
6. 水平居中：.nav.justify-content-center 
7. 水平居右：.nav.justify-content-end 
8. 頁籤顯示：.nav.nav-tabs 、.nav.nav-pills
9. 填充和對齊：.nav.nav-fill 、.nav.nav-justified 
10. 範例：https://webugm.github.io/bootstrap4/navs.html

二、導航列

1. http://bootstrap.hexschool.com/docs/4.0/components/navbar/
2. 包裝：nav.navbar
3. 品牌：a.navbar-brand
4. 選單：ul.navbar-nav => 項目：li.nav-item => 連結：a.nav-link
5. 展開顯示：.navbar-expand{-sm|-md|-lg|-xl}
6. 顯示樣式：.navbar-light 、.bg-light

三、響應式導航列

1. 包裝：.collapse.navbar-collapse 指定id navbar-content
2. 切換開關：

         <button class="navbar-toggler" data-toggle="collapse" data-target="#navbar-content">
           <span class="navbar-toggler-icon"></span>
         </button>

    

3. 導航位置：
   fixed-top、fixed-bottom、sticky-top

四、下拉選單

      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>

五、直接套用

<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <a class="navbar-brand" href="#">Navbar</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Link</a>
      </li>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
      <li class="nav-item">
        <a class="nav-link disabled" href="#">Disabled</a>
      </li>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
    </form>
  </div>
</nav>