Add Font Awesome Icons to our Buttons

说明：

Font Awesome 是一个非常方便的图标库。这些图标都是矢量图形，被保存在 .svg 的文件格式中。这些图标就和字体一样，你可以通过像素单位指定它们的大小，它们将会继承其父HTML元素的字体大小。

你可以将 Font Awesome 图标库增添至任何一个应用中，方法很简单，只需要在你的 HTML 头部增加下列代码即可：

<link rel="stylesheet" href="//cdn.bootcss.com/font-awesome/4.2.0/css/font-awesome.min.css"/>

不过，我们已经事先在幕后为此页面添加了该功能。（不必重复添加上面这段代码）

i 元素起初一般是让其它元素有斜体(italic)的功能，不过现在一般用来指代图标。你可以将 Font Awesome 中的 class 属性添加到 i 元素中，把它变成一个图标，比如：

<i class="fa fa-info-circle"></i>

你可以通过 Font Awesome 库增加一个 thumbs-up 图标到你的 like 按钮中，方法是在i 元素中增加 class 属性 fa 和 fa-thumbs-up。

原始代码：

<link href="//fonts.gdgdocs.org/css?family=Lobster" rel="stylesheet" type="text/css">
<style>
  h2 {
    font-family: Lobster, Monospace;
  }

  .thick-green-border {
    border-color: green;
    border-width: 10px;
    border-style: solid;
    border-radius: 50%;
  }
</style>

<div class="container-fluid">
  <div class="row">
    <div class="col-xs-8">
      <h2 class="text-primary text-center">CatPhotoApp</h2>
    </div>
    <div class="col-xs-4">
      <a href="#"><img class="img-responsive thick-green-border" src="/images/relaxing-cat.jpg"></a>
    </div>
  </div>
  <img src="/images/running-cat.jpg" class="img-responsive">
  <div class="row">
    <div class="col-xs-4">
      <button class="btn btn-block btn-primary">Like</button>
    </div>
    <div class="col-xs-4">
      <button class="btn btn-block btn-info">Info</button>
    </div>
    <div class="col-xs-4">
      <button class="btn btn-block btn-danger">Delete</button>
    </div>
  </div>
  <p>Things cats <span class="text-danger">love:</span></p>
  <ul>
    <li>cat nip</li>
    <li>laser pointers</li>
    <li>lasagna</li>
  </ul>
  <p>Top 3 things cats hate:</p>
  <ol>
    <li>flea treatment</li>
    <li>thunder</li>
    <li>other cats</li>
  </ol>
  <form action="/submit-cat-photo">
    <label><input type="radio" name="indoor-outdoor"> Indoor</label>
    <label><input type="radio" name="indoor-outdoor"> Outdoor</label>
    <label><input type="checkbox" name="personality"> Loving</label>
    <label><input type="checkbox" name="personality"> Lazy</label>
    <label><input type="checkbox" name="personality"> Crazy</label>
    <input type="text" placeholder="cat photo URL" required>
    <button type="submit">Submit</button>
  </form>
</div>

调试代码：

<link href="//fonts.gdgdocs.org/css?family=Lobster" rel="stylesheet" type="text/css">
<style>
  h2 {
    font-family: Lobster, Monospace;
  }

  .thick-green-border {
    border-color: green;
    border-width: 10px;
    border-style: solid;
    border-radius: 50%;
  }
</style>

<div class="container-fluid">
  <div class="row">
    <div class="col-xs-8">
      <h2 class="text-primary text-center">CatPhotoApp</h2>
    </div>
    <div class="col-xs-4">
      <a href="#"><img class="img-responsive thick-green-border" src="/images/relaxing-cat.jpg"></a>
    </div>
  </div>
  <img src="/images/running-cat.jpg" class="img-responsive">
  <div class="row">
    <div class="col-xs-4">    
      <button class="btn btn-block btn-primary"><i class="fa fa-thumbs-up"></i>Like</button>
    </div>
    <div class="col-xs-4">
      <button class="btn btn-block btn-info">Info</button>
    </div>
    <div class="col-xs-4">
      <button class="btn btn-block btn-danger">Delete</button>
    </div>
  </div>
  <p>Things cats <span class="text-danger">love:</span></p>
  <ul>
    <li>cat nip</li>
    <li>laser pointers</li>
    <li>lasagna</li>
  </ul>
  <p>Top 3 things cats hate:</p>
  <ol>
    <li>flea treatment</li>
    <li>thunder</li>
    <li>other cats</li>
  </ol>
  <form action="/submit-cat-photo">
    <label><input type="radio" name="indoor-outdoor"> Indoor</label>
    <label><input type="radio" name="indoor-outdoor"> Outdoor</label>
    <label><input type="checkbox" name="personality"> Loving</label>
    <label><input type="checkbox" name="personality"> Lazy</label>
    <label><input type="checkbox" name="personality"> Crazy</label>
    <input type="text" placeholder="cat photo URL" required>
    <button type="submit">Submit</button>
  </form>
</div>