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320 lines
11 KiB
Markdown
320 lines
11 KiB
Markdown
---
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layout: docs
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title: Utility classes
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group: components
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---
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Bootstrap includes dozens of utilities—classes with a single purpose. They're designed to reduce the frequency of highly repetitive declarations in your CSS while allowing for quick and easy development.
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## Contents
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* Will be replaced with the ToC, excluding the "Contents" header
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{:toc}
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## Spacing
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Assign `margin` or `padding` to an element or a subset of its sides with shorthand classes. Includes support for individual properties, all properties, and vertical and horizontal properties. All classes are multiples on the global default value, `1rem`.
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### Margin
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{% highlight scss %}
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.m-a-0 { margin: 0 !important; }
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.m-t-0 { margin-top: 0 !important; }
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.m-r-0 { margin-right: 0 !important; }
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.m-b-0 { margin-bottom: 0 !important; }
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.m-l-0 { margin-left: 0 !important; }
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.m-x-0 { margin-right: 0 !important; margin-left: 0 !important; }
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.m-y-0 { margin-top: 0 !important; margin-bottom: 0 !important; }
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.m-a { margin: $spacer !important; }
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.m-t { margin-top: $spacer-y !important; }
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.m-r { margin-right: $spacer-x !important; }
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.m-b { margin-bottom: $spacer-y !important; }
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.m-l { margin-left: $spacer-x !important; }
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.m-x { margin-right: $spacer-x !important; margin-left: $spacer-x !important; }
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.m-y { margin-top: $spacer-y !important; margin-bottom: $spacer-y !important; }
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.m-x-auto { margin-right: auto !important; margin-left: auto !important; }
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.m-a-md { margin: ($spacer * 1.5) !important; }
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.m-t-md { margin-top: ($spacer-y * 1.5) !important; }
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.m-r-md { margin-right: ($spacer-y * 1.5) !important; }
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.m-b-md { margin-bottom: ($spacer-y * 1.5) !important; }
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.m-l-md { margin-left: ($spacer-y * 1.5) !important; }
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.m-x-md { margin-right: ($spacer-x * 1.5) !important; margin-left: ($spacer-x * 1.5) !important; }
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.m-y-md { margin-top: ($spacer-y * 1.5) !important; margin-bottom: ($spacer-y * 1.5) !important; }
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.m-a-lg { margin: ($spacer * 3) !important; }
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.m-t-lg { margin-top: ($spacer-y * 3) !important; }
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.m-r-lg { margin-right: ($spacer-y * 3) !important; }
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.m-b-lg { margin-bottom: ($spacer-y * 3) !important; }
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.m-l-lg { margin-left: ($spacer-y * 3) !important; }
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.m-x-lg { margin-right: ($spacer-x * 3) !important; margin-left: ($spacer-x * 3) !important; }
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.m-y-lg { margin-top: ($spacer-y * 3) !important; margin-bottom: ($spacer-y * 3) !important; }
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{% endhighlight %}
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### Padding
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{% highlight scss %}
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.p-a-0 { padding: 0 !important; }
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.p-t-0 { padding-top: 0 !important; }
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.p-r-0 { padding-right: 0 !important; }
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.p-b-0 { padding-bottom: 0 !important; }
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.p-l-0 { padding-left: 0 !important; }
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.p-x-0 { padding-left: 0 !important; padding-right: 0 !important; }
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.p-y-0 { padding-top: 0 !important; padding-bottom: 0 !important; }
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.p-a { padding: $spacer !important; }
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.p-t { padding-top: $spacer-y !important; }
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.p-r { padding-right: $spacer-x !important; }
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.p-b { padding-bottom: $spacer-y !important; }
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.p-l { padding-left: $spacer-x !important; }
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.p-x { padding-right: $spacer-x !important; padding-left: $spacer-x !important; }
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.p-y { padding-top: $spacer-y !important; padding-bottom: $spacer-y !important; }
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.p-a-md { padding: ($spacer * 1.5) !important; }
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.p-t-md { padding-top: ($spacer-y * 1.5) !important; }
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.p-r-md { padding-right: ($spacer-y * 1.5) !important; }
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.p-b-md { padding-bottom: ($spacer-y * 1.5) !important; }
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.p-l-md { padding-left: ($spacer-y * 1.5) !important; }
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.p-x-md { padding-right: ($spacer-x * 1.5) !important; padding-left: ($spacer-x * 1.5) !important; }
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.p-y-md { padding-top: ($spacer-y * 1.5) !important; padding-bottom: ($spacer-y * 1.5) !important; }
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.p-a-lg { padding: ($spacer * 3) !important; }
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.p-t-lg { padding-top: ($spacer-y * 3) !important; }
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.p-r-lg { padding-right: ($spacer-y * 3) !important; }
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.p-b-lg { padding-bottom: ($spacer-y * 3) !important; }
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.p-l-lg { padding-left: ($spacer-y * 3) !important; }
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.p-x-lg { padding-right: ($spacer-x * 3) !important; padding-left: ($spacer-x * 3) !important; }
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.p-y-lg { padding-top: ($spacer-y * 3) !important; padding-bottom: ($spacer-y * 3) !important; }
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{% endhighlight %}
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## Text alignment
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Easily realign text to components with text alignment classes.
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{% example html %}
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<p class="text-left">Left aligned text.</p>
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<p class="text-center">Center aligned text.</p>
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<p class="text-right">Right aligned text.</p>
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<p class="text-justify">Justified text.</p>
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<p class="text-nowrap">No wrap text.</p>
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{% endexample %}
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## Text transform
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Transform text in components with text capitalization classes.
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{% example html %}
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<p class="text-lowercase">Lowercased text.</p>
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<p class="text-uppercase">Uppercased text.</p>
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<p class="text-capitalize">CapiTaliZed text.</p>
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{% endexample %}
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## Contextual colors and backgrounds
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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.
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{% example html %}
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<p class="text-muted">Fusce dapibus, tellus ac cursus commodo, tortor mauris nibh.</p>
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<p class="text-primary">Nullam id dolor id nibh ultricies vehicula ut id elit.</p>
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<p class="text-success">Duis mollis, est non commodo luctus, nisi erat porttitor ligula.</p>
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<p class="text-info">Maecenas sed diam eget risus varius blandit sit amet non magna.</p>
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<p class="text-warning">Etiam porta sem malesuada magna mollis euismod.</p>
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<p class="text-danger">Donec ullamcorper nulla non metus auctor fringilla.</p>
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{% endexample %}
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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.
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{% example html %}
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<div class="bg-primary">Nullam id dolor id nibh ultricies vehicula ut id elit.</div>
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<div class="bg-success">Duis mollis, est non commodo luctus, nisi erat porttitor ligula.</div>
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<div class="bg-info">Maecenas sed diam eget risus varius blandit sit amet non magna.</div>
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<div class="bg-warning">Etiam porta sem malesuada magna mollis euismod.</div>
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<div class="bg-danger">Donec ullamcorper nulla non metus auctor fringilla.</div>
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<div class="bg-inverse">Cras mattis consectetur purus sit amet fermentum.</div>
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{% endexample %}
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{% callout info %}
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#### Dealing with specificity
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Sometimes contextual 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 `<div>` with the class.
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{% endcallout %}
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{% callout warning %}
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#### Conveying meaning to assistive technologies
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Ensure that any meaning conveyed through color is also conveyed in a format that is not purely presentational.
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{% endcallout %}
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## Close icon
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Use a generic close icon for dismissing content like modals and alerts. **Be sure to include text for screen readers**, as we've done with `aria-label`.
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{% example html %}
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<button type="button" class="close" aria-label="Close">
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<span aria-hidden="true">×</span>
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</button>
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{% endexample %}
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## Floats
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Float an element to the left or right with a class. `!important` is included to avoid specificity issues. Classes can also be used as mixins.
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{% example html %}
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<div class="pull-left">Float left</div>
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<div class="pull-right">Float right</div>
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{% endexample %}
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{% highlight scss %}
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// Classes
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.pull-left {
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float: left !important;
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}
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.pull-right {
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float: right !important;
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}
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// Usage as mixins
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.element {
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@include pull-left;
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}
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.another-element {
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@include pull-right;
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}
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{% endhighlight %}
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## Center content
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Set an element to `display: block;` and center via `margin`. Available as a mixin and class.
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{% example html %}
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<div class="center-block">Centered block</div>
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{% endexample %}
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{% highlight scss %}
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// Class
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.center-block {
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display: block;
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margin-left: auto;
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margin-right: auto;
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}
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// Usage as a mixin
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.element {
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@include center-block;
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}
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{% endhighlight %}
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Easily clear `float`s by adding `.clearfix` **to the parent element**. Utilizes [the micro clearfix](http://nicolasgallagher.com/micro-clearfix-hack/) as popularized by Nicolas Gallagher. Can also be used as a mixin.
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{% highlight html %}
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<div class="clearfix">...</div>
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{% endhighlight %}
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{% highlight scss %}
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// Mixin itself
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.clearfix() {
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&:before,
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&:after {
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content: " ";
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display: table;
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}
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&:after {
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clear: both;
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}
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}
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// Usage as a mixin
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.element {
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@include clearfix;
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}
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{% endhighlight %}
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## Invisible content
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The `.invisible` class can be used to toggle only the visibility of an element, meaning its `display` is not modified and the element can still affect the flow of the document.
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{% highlight html %}
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<div class="invisible">...</div>
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{% endhighlight %}
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{% highlight scss %}
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// Class
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.invisible {
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visibility: hidden;
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}
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// Usage as a mixin
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.element {
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.invisible();
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}
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{% endhighlight %}
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## Screen readers and keyboard users
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Hide an element to all devices **except screen readers** with `.sr-only`. Combine `.sr-only` with `.sr-only-focusable` to show the element again when it's focused (e.g. by a keyboard-only user). Can also be used as mixins.
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{% comment %}
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Necessary for following [accessibility best practices](../getting-started/#accessibility).
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{% endcomment %}
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{% highlight html %}
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<a class="sr-only sr-only-focusable" href="#content">Skip to main content</a>
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{% endhighlight %}
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{% highlight scss %}
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// Usage as a mixin
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.skip-navigation {
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@include sr-only;
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@include sr-only-focusable;
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}
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{% endhighlight %}
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## Image replacement
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Utilize the `.text-hide` class or mixin to help replace an element's text content with a background image.
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{% highlight html %}
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<h1 class="text-hide">Custom heading</h1>
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{% endhighlight %}
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{% highlight scss %}
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// Usage as a mixin
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.heading {
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@include text-hide;
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}
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{% endhighlight %}
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## Responsive embeds
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Allow browsers to determine video or slideshow dimensions based on the width of their containing block by creating an intrinsic ratio that will properly scale on any device.
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Rules are directly applied to `<iframe>`, `<embed>`, `<video>`, and `<object>` elements; optionally use an explicit descendant class `.embed-responsive-item` when you want to match the styling for other attributes.
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**Pro-Tip!** You don't need to include `frameborder="0"` in your `<iframe>`s as we override that for you.
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{% example html %}
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<div class="embed-responsive embed-responsive-16by9">
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<iframe class="embed-responsive-item" src="//www.youtube.com/embed/zpOULjyy-n8?rel=0" allowfullscreen></iframe>
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</div>
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{% endexample %}
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Aspect ratios can be customized with modifier classes.
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{% highlight html %}
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<!-- 21:9 aspect ratio -->
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<div class="embed-responsive embed-responsive-21by9">
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<iframe class="embed-responsive-item" src="..."></iframe>
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</div>
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<!-- 16:9 aspect ratio -->
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<div class="embed-responsive embed-responsive-16by9">
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<iframe class="embed-responsive-item" src="..."></iframe>
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</div>
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<!-- 4:3 aspect ratio -->
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<div class="embed-responsive embed-responsive-4by3">
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<iframe class="embed-responsive-item" src="..."></iframe>
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</div>
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{% endhighlight %}
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