bootstrap顶部导航遮挡下面内容的解决办法

使用bootstrap设置顶部导航，并将导航栏固定，代码如下：

 <nav class="navbar navbar-expand-lg navbar-light bg-light fixed-top">
   <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo03" aria-controls="navbarTogglerDemo03" aria-expanded="false" aria-label="Toggle navigation">
     <span class="navbar-toggler-icon"></span>
   </button>
   <a class="navbar-brand" href="#">Navbar</a>

   <div class="collapse navbar-collapse" id="navbarTogglerDemo03">
     <ul class="navbar-nav mr-auto mt-2 mt-lg-0">
       <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">
         <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">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>
 <div class="container-fluid">
   <h1>我的第一个 Bootstrap 页面</h1>
   <p>使用了 .container-fluid，100% 宽度，占据全部视口（viewport）的容器。</p>
 </div>

代码文本：

<nav class="navbar navbar-expand-lg navbar-light bg-light fixed-top">
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo03" aria-controls="navbarTogglerDemo03" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<a class="navbar-brand" href="#">Navbar</a>

<div class="collapse navbar-collapse" id="navbarTogglerDemo03">
<ul class="navbar-nav mr-auto mt-2 mt-lg-0">
<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">
<a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">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>
<div class="container-fluid">
<h1>我的第一个 Bootstrap 页面</h1>
<p>使用了 .container-fluid，100% 宽度，占据全部视口（viewport）的容器。</p>
</div>

在浏览器里预览，发现导航会把下面的内容遮挡住，发现是因为导航设置了fixed-top，而下面的模块样式没有处理，所以就遮挡住了下面的内容

解决办法：
1.去掉导航的fixed-top样式类
2.添加样式ody{margin-top:60px;/* 或者其他更大的值 */}

done!