<hr>标签失效问题

<div class="jumbotron">

        <h1>Hello, world!</h1>

        <hr>

        <p>This is a template for a simple marketing or informational website. It includes a large callout called a jumbotron and three supporting pieces of content. Use it as a starting point to create something more unique.</p>

<hr>zai bootstrap中是不是不起作用??