Bootstrap/docs/components/utilities.md

layout	title	group
docs	Utility classes	components

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.

Contents

• Will be replaced with the ToC, excluding the "Contents" header {:toc}

Spacing

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.

The classes are named using the format: {property}-{sides}-{size}

Where property is one of:

• m - for classes that set margin
• p - for classes that set padding

Where sides is one of:

• t - for classes that set margin-top or padding-top
• b - for classes that set margin-bottom or padding-bottom
• l - for classes that set margin-left or padding-left
• r - for classes that set margin-right or padding-right
• x - for classes that set both *-left and *-right
• y - for classes that set both *-top and *-bottom
• a - for classes that set a margin or padding on all 4 sides of the element

Where size is one of:

• 0 - for classes that eliminate the margin or padding by setting it to 0
• 1 - (by default) for classes that set the margin or padding to $spacer-x or $spacer-y
• 2 - (by default) for classes that set the margin or padding to $spacer-x * 1.5 or $spacer-y * 1.5
• 3 - (by default) for classes that set the margin or padding to $spacer-x * 3 or $spacer-y * 3

(You can add more sizes by adding entries to the $spacers Sass map variable.)

Here are some representative examples of these classes:

{% highlight scss %} .m-t-0 { margin-top: 0 !important; }

.m-l-1 { margin-left: $spacer-x !important; }

.p-x-2 { padding-left: ($spacer-x * 1.5) !important; padding-right: ($spacer-x * 1.5) !important; }

.p-a-3 { padding: ($spacer-y * 3) ($spacer-x * 3) !important; } {% endhighlight %}

Horizontal centering

Additionally, Bootstrap also includes an .m-x-auto class for horizontally centering fixed-width block level content by setting the horizontal margins to auto.

Centered element

{% highlight html %}

Centered element

{% endhighlight %}

Text alignment

Easily realign text to components with text alignment classes.

{% example html %}

Justified text.

No wrap text.

{% endexample %}

For left, right, and center alignment, responsive classes are available that use the same viewport width breakpoints as the grid system.

{% example html %}

Left aligned text on all viewport sizes.

Center aligned text on all viewport sizes.

Right aligned text on all viewport sizes.

Left aligned text on viewports sized SM (small) or wider.

Left aligned text on viewports sized MD (medium) or wider.

Left aligned text on viewports sized LG (large) or wider.

Left aligned text on viewports sized XL (extra-large) or wider.

{% endexample %}

Text transform

Transform text in components with text capitalization classes.

{% example html %}

Lowercased text.

Uppercased text.

CapiTaliZed text.

{% endexample %}

Note how text-capitalize only changes the first letter of each word, leaving the case of any other letters unaffected.

Font weight and italics

Quickly change the weight (boldness) of text or italicize text.

{% example html %}

Bold text.

Normal weight text.

Italic text.

{% endexample %}

Contextual colors and backgrounds

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 %}

Contextual text classes also work well on anchors with the provided hover and focus states.

{% example html %} Muted link Primary link Success link Info link Warning link Danger link {% endexample %}

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.

Cras mattis consectetur purus sit amet fermentum.

{% endexample %}

{% callout info %}

Dealing with specificity

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. {% endcallout %}

{% capture callout-include %}{% include callout-warning-color-assistive-technologies.md %}{% endcapture %} {{ callout-include | markdownify }}

Close icon

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.

{% example html %} × {% endexample %}

Responsive floats

These utility classes float an element to the left or right, or disable floating, based on the current viewport size using the CSS float property. !important is included to avoid specificity issues. These use the same viewport width breakpoints as the grid system.

Two similar non-responsive mixins (pull-left and pull-right) are also available.

{% example html %}

Float left on all viewport sizes

Float right on all viewport sizes

Don't float on all viewport sizes

Float left on viewports sized SM (small) or wider

Float left on viewports sized MD (medium) or wider

Float left on viewports sized LG (large) or wider

Float left on viewports sized XL (extra-large) or wider

{% endexample %}

{% highlight scss %} // Related simple non-responsive mixins .element { @include pull-left; } .another-element { @include pull-right; } {% endhighlight %}

Clearfix

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 %}

Fixed positioning

The .pos-f-t class can be used to easily position elements at the top of the viewport and make them as wide as the viewport. Be sure you understand the ramifications of fixed-position elements within your project. Here's how the class is defined:

{% highlight scss %} .pos-f-t { position: fixed; top: 0; right: 0; left: 0; z-index: $zindex-navbar-fixed; } {% 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 { @include invisible; } {% endhighlight %}

Screen readers and keyboard users

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.

{% comment %} Necessary for following accessibility best practices. {% endcomment %}

{% 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 %}

Responsive embeds

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.

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.

Pro-Tip! You don't need to include frameborder="0" in your <iframe>s as we override that for you.

{% example html %}

{% endexample %}

Aspect ratios can be customized with modifier classes.

{% highlight html %}

{% endhighlight %}