twbs--bootstrap/docs/components/utilities.md

layout	title
page	Utility classes

Bootstrap includes dozens of utilities—classes with a single purpose. They're designed to keep the number of declarations in your CSS down while allowing for quick and easy development.

Text alignment

Easily realign text to components with text alignment classes.

{% example html %}

Left aligned text.

Center aligned text.

Right aligned text.

Justified text.

No wrap text.

{% endexample %}

Text transform

Transform text in components with text capitalization classes.

{% example html %}

Lowercased text.

Uppercased text.

Capitalized text.

{% endexample %}

Contextual colors

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.

{% example html %}

Fusce dapibus, tellus ac cursus commodo, tortor mauris nibh.

Nullam id dolor id nibh ultricies vehicula ut id elit.

Duis mollis, est non commodo luctus, nisi erat porttitor ligula.

Maecenas sed diam eget risus varius blandit sit amet non magna.

Etiam porta sem malesuada magna mollis euismod.

Donec ullamcorper nulla non metus auctor fringilla.

{% endexample %}

{% callout info %}

Dealing with specificity

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 <span> with the class. {% endcallout %}

{% callout warning %}

Conveying meaning to assistive technologies

Using color to add meaning only provides a visual indication, which will not be conveyed to users of assistive technologies – such as screen readers. Ensure that information denoted by the color is either obvious from the content itself (the contextual colors are only used to reinforce meaning that is already present in the text/markup), or is included through alternative means, such as additional text hidden with the .sr-only class. {% endcallout %}

Contextual backgrounds

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.

{% example html %}

Nullam id dolor id nibh ultricies vehicula ut id elit.

Duis mollis, est non commodo luctus, nisi erat porttitor ligula.

Maecenas sed diam eget risus varius blandit sit amet non magna.

Etiam porta sem malesuada magna mollis euismod.

Donec ullamcorper nulla non metus auctor fringilla.

{% endexample %}

{% callout info %}

Dealing with specificity

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 <div> with the class. {% endcallout %}

{% callout warning %}

Conveying meaning to assistive technologies

As with contextual colors, ensure that any meaning conveyed through color is also conveyed in a format that is not purely presentational. {% endcallout %}

Close icon

Use a generic close icon for dismissing content like modals and alerts. Be sure to include screen reader text when you can as we've done with .sr-only.

{% example html %} × Close {% endexample %}

Floats

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.

{% example html %}

Float left

Float right

{% endexample %}

{% highlight scss %} // Classes .pull-left { float: left !important; } .pull-right { float: right !important; }

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

Center content

Set an element to display: block; and center via margin. Available as a mixin and class.

{% example html %}

Centered block

{% endexample %}

{% highlight scss %} // Class .center-block { display: block; margin-left: auto; margin-right: auto; }

// Usage as a mixin .element { @include center-block; } {% endhighlight %}

Easily clear floats by adding .clearfix to the parent element. Utilizes the micro clearfix as popularized by Nicolas Gallagher. Can also be used as a mixin.

{% highlight html %}

...

{% endhighlight %}

{% highlight scss %} // Mixin itself .clearfix() { &:before, &:after { content: " "; display: table; } &:after { clear: both; } }

// Usage as a mixin .element { @include clearfix; } {% endhighlight %}

Hidden content

Hide any HTML element with the [hidden] attribute. Previously, v3.x included a .hidden class that forced toggled content. However, we removed it due to conflicts with jQuery's hide() function. It's taken from PureCSS.

Furthermore, .invisible can be used to toggle the visibility of an element, meaning its display is not modified and the element can still affect the flow of the document.

{% highlight html %} {% endhighlight %}

Invisible content

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.

{% highlight html %}

...

{% endhighlight %}

{% highlight scss %} // Class .invisible { visibility: hidden; }

// Usage as a mixin .element { .invisible(); } {% endhighlight %}

Screen readers

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). Necessary for following accessibility best practices. Can also be used as mixins.

{% highlight html %} Skip to main content {% endhighlight %}

{% highlight scss %} // Usage as a mixin .skip-navigation { @include sr-only; @include sr-only-focusable; } {% endhighlight %}

Image replacement

Utilize the .text-hide class or mixin to help replace an element's text content with a background image.

{% highlight html %}

Custom heading

{% endhighlight %}

{% highlight scss %} // Usage as a mixin .heading { @include text-hide; } {% endhighlight %}