警告提示框：

警报是一组颜色控件（共八个颜色样式），可用于任何长度的文本，以及可选的关闭按钮，系统提供8个可用的正确的样式。

八种颜色样式：

  1. <div class="alert alert-primary" role="alert">
  2.         A simple primary alert—check it out!
  3.     </div>
  4.     <div class="alert alert-secondary" role="alert">
  5.         A simple secondary alert—check it out!
  6.     </div>
  7.     <div class="alert alert-success" role="alert">
  8.         A simple success alert—check it out!
  9.     </div>
  10.     <div class="alert alert-danger" role="alert">
  11.         A simple danger alert—check it out!
  12.     </div>
  13.     <div class="alert alert-warning" role="alert">
  14.         A simple warning alert—check it out!
  15.     </div>
  16.     <div class="alert alert-info" role="alert">
  17.         A simple info alert—check it out!
  18.     </div>
  19.     <div class="alert alert-light" role="alert">
  20.         A simple light alert—check it out!
  21.     </div>
  22.     <div class="alert alert-dark" role="alert">
  23.         A simple dark alert—check it out!
  24.     </div>

关闭警告:

<div class="alert alert-warning alert-dismissible fade show" role="alert">
    <strong>Holy guacamole!</strong> You should check in on some of those fields below.
    <button type="button" class="close" data-dismiss="alert" aria-label="Close">
        <span aria-hidden="true">&times;</span>
    </button>
</div>

关闭警告效果：

图片.png
点击（x）可以关闭