Bootstrap/docs/_includes/css/helpers.html

<div class="bs-docs-section">
  <h1 id="helper-classes" class="page-header">Helper classes</h1>

  <h3 id="helper-classes-colors">Contextual colors</h3>
  <p>Convey meaning through color with a handful of emphasis utility classes. These may also be applied to links and will darken on hover just like our default link styles.</p>
  <div class="bs-example">
    <p class="text-muted">Fusce dapibus, tellus ac cursus commodo, tortor mauris nibh.</p>
    <p class="text-primary">Nullam id dolor id nibh ultricies vehicula ut id elit.</p>
    <p class="text-success">Duis mollis, est non commodo luctus, nisi erat porttitor ligula.</p>
    <p class="text-info">Maecenas sed diam eget risus varius blandit sit amet non magna.</p>
    <p class="text-warning">Etiam porta sem malesuada magna mollis euismod.</p>
    <p class="text-danger">Donec ullamcorper nulla non metus auctor fringilla.</p>
  </div>
{% highlight html %}
<p class="text-muted">...</p>
<p class="text-primary">...</p>
<p class="text-success">...</p>
<p class="text-info">...</p>
<p class="text-warning">...</p>
<p class="text-danger">...</p>
{% endhighlight %}
  <div class="bs-callout bs-callout-info">
    <h4>Dealing with specificity</h4>
    <p>Sometimes emphasis classes cannot be applied due to the specificity of another selector. In most cases, a sufficient workaround is to wrap your text in a <code>&lt;span&gt;</code> with the class.</p>
  </div>

  <h3 id="helper-classes-backgrounds">Contextual backgrounds</h3>
  <p>Similar to the contextual text color classes, easily set the background of an element to any contextual class. Anchor components will darken on hover, just like the text classes.</p>
  <div class="bs-example bs-example-bg-classes">
    <p class="bg-primary">Nullam id dolor id nibh ultricies vehicula ut id elit.</p>
    <p class="bg-success">Duis mollis, est non commodo luctus, nisi erat porttitor ligula.</p>
    <p class="bg-info">Maecenas sed diam eget risus varius blandit sit amet non magna.</p>
    <p class="bg-warning">Etiam porta sem malesuada magna mollis euismod.</p>
    <p class="bg-danger">Donec ullamcorper nulla non metus auctor fringilla.</p>
  </div>
{% highlight html %}
<p class="bg-primary">...</p>
<p class="bg-success">...</p>
<p class="bg-info">...</p>
<p class="bg-warning">...</p>
<p class="bg-danger">...</p>
{% endhighlight %}
  <div class="bs-callout bs-callout-info">
    <h4>Dealing with specificity</h4>
    <p>Sometimes contextual background classes cannot be applied due to the specificity of another selector. In some cases, a sufficient workaround is to wrap your element's content in a <code>&lt;div&gt;</code> with the class.</p>
  </div>

  <h3 id="helper-classes-close">Close icon</h3>
  <p>Use the generic close icon for dismissing content like modals and alerts.</p>
  <div class="bs-example">
    <p><button type="button" class="close"><span aria-hidden="true">&times;</span><span class="sr-only">Close</span></button></p>
  </div>
{% highlight html %}
<button type="button" class="close"><span aria-hidden="true">&times;</span><span class="sr-only">Close</span></button>
{% endhighlight %}


  <h3 id="helper-classes-carets">Carets</h3>
  <p>Use carets to indicate dropdown functionality and direction. Note that the default caret will reverse automatically in <a href="../components/#btn-dropdowns-dropup">dropup menus</a>.</p>
  <div class="bs-example">
    <span class="caret"></span>
  </div>
{% highlight html %}
<span class="caret"></span>
{% endhighlight %}


  <h3 id="helper-classes-floats">Quick floats</h3>
  <p>Float an element to the left or right with a class. <code>!important</code> is included to avoid specificity issues. Classes can also be used as mixins.</p>
{% highlight html %}
<div class="pull-left">...</div>
<div class="pull-right">...</div>
{% endhighlight %}
{% highlight scss %}
// Classes
.pull-left {
  float: left !important;
}
.pull-right {
  float: right !important;
}

// Usage as mixins
.element {
  .pull-left();
}
.another-element {
  .pull-right();
}
{% endhighlight %}

  <div class="bs-callout bs-callout-warning">
    <h4>Not for use in navbars</h4>
    <p>To align components in navbars with utility classes, use <code>.navbar-left</code> or <code>.navbar-right</code> instead. <a href="../components/#navbar-component-alignment">See the navbar docs</a> for details.</p>
  </div>


  <h3 id="helper-classes-center">Center content blocks</h3>
  <p>Set an element to <code>display: block</code> and center via <code>margin</code>. Available as a mixin and class.</p>
{% highlight html %}
<div class="center-block">...</div>
{% endhighlight %}
{% highlight scss %}
// Classes
.center-block {
  display: block;
  margin-left: auto;
  margin-right: auto;
}

// Usage as mixins
.element {
  .center-block();
}
{% endhighlight %}


  <h3 id="helper-classes-clearfix">Clearfix</h3>
  <p>Clear the <code>float</code> on any element with the <code>.clearfix</code> class. Utilizes <a href="http://nicolasgallagher.com/micro-clearfix-hack/">the micro clearfix</a> as popularized by Nicolas Gallagher. Can also be used as a mixin.</p>
{% highlight html %}
<!-- Usage as a class -->
<div class="clearfix">...</div>
{% endhighlight %}
{% highlight scss %}
// Mixin itself
.clearfix() {
  &:before,
  &:after {
    content: " ";
    display: table;
  }
  &:after {
    clear: both;
  }
}

// Usage as a Mixin
.element {
  .clearfix();
}
{% endhighlight %}


  <h3 id="helper-classes-show-hide">Showing and hiding content</h3>
  <p>Force an element to be shown or hidden (<strong>including for screen readers</strong>) with the use of <code>.show</code> and <code>.hidden</code> classes. These classes use <code>!important</code> to avoid specificity conflicts, just like the <a href="#helper-classes-floats">quick floats</a>. They are only available for block level toggling. They can also be used as mixins.</p>
  <p><code>.hide</code> is available, but it does not always affect screen readers and is <strong>deprecated</strong> as of v3.0.1. Use <code>.hidden</code> or <code>.sr-only</code> instead.</p>
  <p>Furthermore, <code>.invisible</code> can be used to toggle only the visibility of an element, meaning its <code>display</code> is not modified and the element can still affect the flow of the document.</p>
{% highlight html %}
<div class="show">...</div>
<div class="hidden">...</div>
{% endhighlight %}
{% highlight scss %}
// Classes
.show {
  display: block !important;
}
.hidden {
  display: none !important;
  visibility: hidden !important;
}
.invisible {
  visibility: hidden;
}

// Usage as mixins
.element {
  .show();
}
.another-element {
  .hidden();
}
{% endhighlight %}


  <h3 id="helper-classes-screen-readers">Screen reader and keyboard navigation content</h3>
  <p>Hide an element to all devices <strong>except screen readers</strong> with <code>.sr-only</code>. Combine <code>.sr-only</code> with <code>.sr-only-focusable</code> to show the element again when it's focused (e.g. by a keyboard-only user). Necessary for following <a href="../getting-started/#accessibility">accessibility best practices</a>. Can also be used as mixins.</p>
{% highlight html %}
<a class="sr-only sr-only-focusable" href="#content">Skip to main content</a>
{% endhighlight %}
{% highlight scss %}
// Usage as a Mixin
.skip-navigation {
  .sr-only();
  .sr-only-focusable();
}
{% endhighlight %}


  <h3 id="helper-classes-image-replacement">Image replacement</h3>
  <p>Utilize the <code>.text-hide</code> class or mixin to help replace an element's text content with a background image.</p>
{% highlight html %}
<h1 class="text-hide">Custom heading</h1>
{% endhighlight %}
  {% highlight scss %}
// Usage as a Mixin
.heading {
  .text-hide();
}
{% endhighlight %}
</div>