在引导程序中的“.container-fluid”和“行”中将“.img-responsive”居中？

Question

我不希望这里的答案对 21 世纪对计算机科学的理解有多大帮助，但我感谢社区的帮助。

我有一个图像，我试图在引导程序中居中。它位于 .container-fluid、.row 和带有 .offset-xs-3 的 .col-xs-6 中。 <img...> 本身就是 .img-responsive。你可以在这个 codepen 上看到这个项目：http://codepen.io/NotAnAmbiTurner/pen/GrGmaq?editors=1000。

图像未居中 - 我应该能够获得随视口宽度（a la SVG）缩放并位于页面中间的图像。我似乎无法做到这一点。

我想知道这是否与我从保管箱中获取“原始”图像作为我的src、图像是.jpg 或某种组合这一事实有关？再说一次，我是个菜鸟，所以同样有可能在我似乎找不到的地方有一个错字。我已经阅读了引导文档，并且各种 SO 问题都无济于事。我找到的唯一解决方案是从容器和行中删除<img...>，并分配... class="centered-block" ...。但是，除非我从根本上误解了某些东西，否则（1）我不应该这样做，并且（2）我不想通过抨击来了解我的概念错误在任何情况下是什么，以供我自己学习。

PS - 完全不相关，但我的 <a ...></a> 标签似乎不可点击。如果有人在那里有任何想法，那也很棒。

事实证明，基本问题是 CodePen 依赖于 Bootstrap 4，而不是（如我所假设的）Bootstrap 3。

Answer 1

您正在使用 Bootstrap 3 中的类，但从 Bootstrap 4 加载样式表；它们并非全面兼容。 img-responsive 以及 col-xs-* 类不再存在。请参阅Images 和Grid Options。

注意：您的链接将不起作用，因为它们不是有效的 HTML，而且您还使用 h3 validate 您的标记关闭了 h2。

工作示例：

@media (max-width: 480px) {
  h1 {
    font-size: 5vmax;
  }
  h2 {
    font-size: 3.5vmax;
  }
  h3 {
    font-size: 2.5vmax;
  }
  li {
    font-size: 2.5vmax;
  }
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" rel="stylesheet" />

<div class="jumbotron">

  <h1 class="text-primary">Dr. Clair Cameron Patterson</h1>

  <h2 class="text-secondary">The man who first learned the age of the Earth, and helped save a civilization from the dangers of its use of lead.</h2>

  <div class="container-fluid">
    <div class="row">
      <div class="col">
        <img src="https://www.dropbox.com/s/91fw6aazyxzb178/image-for-codecamp-tribute-page.jpg?raw=1" alt="Cartoon Image of Clair Cameron Patterson at Congressional Hearing" class="img-fluid mx-auto d-block" style="padding:1.5vmin">
      </div>
    </div>
  </div>

  <h3>Academics</h3>
  <ul>
    <li>Undergraduate, Grinnell College</li>
    <li>PhD, University of Chicago</li>
    <li>Researcher, California Institute of Technology</li>
  </ul>

  <h3>Brief Timeline</h3>

  <ul>
    <li><strong>1956</strong>: found the earth to be 4.55 Billion years old using <a href="https://en.wikipedia.org/wiki/Lead%E2%80%93lead_dating">lead-lead dating</a> and
      <a href="https://en.wikipedia.org/wiki/Canyon_Diablo_(meteorite)">a fragment of a metorite that fell in Arizona</a>. This calculation has been largely undisturbed since.</li>
    <li><strong>1965</strong>: began campaign against lead in various products, especially gasoline, which at that time was emitting lead into the atmosphere.</li>
    <li><strong>1978</strong>: wrote a 78-page minority opinion as part of a National Research Council (NRC) panel stating that controls on lead in various products had to start immediately, including gasoline, food containers, paint, glazes, and water distribution
      systems.
    </li>
    <li>by the late <strong>1990s</strong>: levels of lead in Americans' blood has dropped by up to 80%. Though connections with Dr. Patterson's work are not clear, as the leading researcher in the area, and constant campaigner against the use of lead, it
      is likely he was a major antecedant of this change.</li>
  </ul>

</div>