Bootstrap导航条的实现

1、打开开发工具，新建‘test.html’在其中写代码如下：

<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>

2、上面的就是实例代码，可以到bootstrap站点查看中文文档

3、在浏览器查看效果如下图

4、上一步虽然实现了导航，但是放在网站一般会觉得太大了，使用container属性的div包住导航条，代码如下：

<div class='container'>

<nav>

</nav>

</div>

5、在浏览器查看效果如下图

6、去掉一些不用的标签，修改代码如下：

<div class="container">

<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>
       </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>
</div>

7、在浏览器查看效果如下图，当然实际中会将brand换成图标img