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<li class="toc-entry toc-h2"><a href="#containers">Containers</a></li>
<li class="toc-entry toc-h2"><a href="#responsive-breakpoints">Responsive breakpoints</a></li>
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<main class="col-12 col-md-9 col-xl-8 py-md-3 pl-md-5 bd-content" role="main">
<h1 class="bd-title" id="content">Overview</h1>
<p class="bd-lead">Components and options for laying out your Bootstrap project, including wrapping containers, a powerful grid system, a flexible media object, and responsive utility classes.</p>
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<h2 id="containers">Containers</h2>
<p>Containers are the most basic layout element in Bootstrap and are <strong>required when using our default grid system</strong>. Choose from a responsive, fixed-width container (meaning its <code class="highlighter-rouge">max-width</code> changes at each breakpoint) or fluid-width (meaning its <code class="highlighter-rouge">100%</code> wide all the time).</p>
<p>While containers <em>can</em> be nested, most layouts do not require a nested container.</p>
<div class="bd-example">
<div class="bd-example-container">
<div class="bd-example-container-header"></div>
<div class="bd-example-container-sidebar"></div>
<div class="bd-example-container-body"></div>
</div>
</div>
<figure class="highlight"><pre><code class="language-html" data-lang="html"><span class="nt">&lt;div</span> <span class="na">class=</span><span class="s">"container"</span><span class="nt">&gt;</span>
<span class="c">&lt;!-- Content here --&gt;</span>
<span class="nt">&lt;/div&gt;</span></code></pre></figure>
<p>Use <code class="highlighter-rouge">.container-fluid</code> for a full width container, spanning the entire width of the viewport.</p>
<div class="bd-example">
<div class="bd-example-container bd-example-container-fluid">
<div class="bd-example-container-header"></div>
<div class="bd-example-container-sidebar"></div>
<div class="bd-example-container-body"></div>
</div>
</div>
<figure class="highlight"><pre><code class="language-html" data-lang="html"><span class="nt">&lt;div</span> <span class="na">class=</span><span class="s">"container-fluid"</span><span class="nt">&gt;</span>
...
<span class="nt">&lt;/div&gt;</span></code></pre></figure>
<h2 id="responsive-breakpoints">Responsive breakpoints</h2>
<p>Since Bootstrap is developed to be mobile first, we use a handful of <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries">media queries</a> to create sensible breakpoints for our layouts and interfaces. These breakpoints are mostly based on minimum viewport widths and allow us to scale up elements as the viewport changes.</p>
<p>Bootstrap primarily uses the following media query ranges—or breakpoints—in our source Sass files for our layout, grid system, and components.</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="c1">// Extra small devices (portrait phones, less than 576px)</span>
<span class="c1">// No media query since this is the default in Bootstrap</span>
<span class="c1">// Small devices (landscape phones, 576px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">576px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Medium devices (tablets, 768px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">768px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Large devices (desktops, 992px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">992px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Extra large devices (large desktops, 1200px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">1200px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span></code></pre></figure>
<p>Since we write our source CSS in Sass, all our media queries are available via Sass mixins:</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="k">@include</span> <span class="nd">media-breakpoint-up</span><span class="p">(</span><span class="n">xs</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-up</span><span class="p">(</span><span class="n">sm</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-up</span><span class="p">(</span><span class="n">md</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-up</span><span class="p">(</span><span class="n">lg</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-up</span><span class="p">(</span><span class="n">xl</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Example usage:</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-up</span><span class="p">(</span><span class="n">sm</span><span class="p">)</span> <span class="p">{</span>
<span class="nc">.some-class</span> <span class="p">{</span>
<span class="nl">display</span><span class="p">:</span> <span class="nb">block</span><span class="p">;</span>
<span class="p">}</span>
<span class="p">}</span></code></pre></figure>
<p>We occasionally use media queries that go in the other direction (the given screen size <em>or smaller</em>):</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="c1">// Extra small devices (portrait phones, less than 576px)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">575</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Small devices (landscape phones, less than 768px)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">767</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Medium devices (tablets, less than 992px)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">991</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Large devices (desktops, less than 1200px)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">1199</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Extra large devices (large desktops)</span>
<span class="c1">// No media query since the extra-large breakpoint has no upper bound on its width</span></code></pre></figure>
<div class="bd-callout bd-callout-info">
<p>Note that since browsers do not currently support <a href="https://www.w3.org/TR/mediaqueries-4/#range-context">range context queries</a>, we work around the limitations of <a href="https://www.w3.org/TR/mediaqueries-4/#mq-min-max"><code class="highlighter-rouge">min-</code> and <code class="highlighter-rouge">max-</code> prefixes</a> and viewports with fractional widths (which can occur under certain conditions on high-dpi devices, for instance) by using values with higher precision for these comparisons.</p>
</div>
<p>Once again, these media queries are also available via Sass mixins:</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="k">@include</span> <span class="nd">media-breakpoint-down</span><span class="p">(</span><span class="n">xs</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-down</span><span class="p">(</span><span class="n">sm</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-down</span><span class="p">(</span><span class="n">md</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-down</span><span class="p">(</span><span class="n">lg</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span></code></pre></figure>
<p>There are also media queries and mixins for targeting a single segment of screen sizes using the minimum and maximum breakpoint widths.</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="c1">// Extra small devices (portrait phones, less than 576px)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">575</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Small devices (landscape phones, 576px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">576px</span><span class="p">)</span> <span class="nf">and</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">767</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Medium devices (tablets, 768px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">768px</span><span class="p">)</span> <span class="nf">and</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">991</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Large devices (desktops, 992px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">992px</span><span class="p">)</span> <span class="nf">and</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">1199</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="c1">// Extra large devices (large desktops, 1200px and up)</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">1200px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span></code></pre></figure>
<p>These media queries are also available via Sass mixins:</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="k">@include</span> <span class="nd">media-breakpoint-only</span><span class="p">(</span><span class="n">xs</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-only</span><span class="p">(</span><span class="n">sm</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-only</span><span class="p">(</span><span class="n">md</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-only</span><span class="p">(</span><span class="n">lg</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span>
<span class="k">@include</span> <span class="nd">media-breakpoint-only</span><span class="p">(</span><span class="n">xl</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span></code></pre></figure>
<p>Similarly, media queries may span multiple breakpoint widths:</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="c1">// Example</span>
<span class="c1">// Apply styles starting from medium devices and up to extra large devices</span>
<span class="k">@media</span> <span class="p">(</span><span class="n">min-width</span><span class="o">:</span> <span class="m">768px</span><span class="p">)</span> <span class="nf">and</span> <span class="p">(</span><span class="n">max-width</span><span class="o">:</span> <span class="m">1199</span><span class="mi">.98px</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span></code></pre></figure>
<p>The Sass mixin for targeting the same screen size range would be:</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="k">@include</span> <span class="nd">media-breakpoint-between</span><span class="p">(</span><span class="n">md</span><span class="o">,</span> <span class="n">xl</span><span class="p">)</span> <span class="p">{</span> <span class="nc">...</span> <span class="p">}</span></code></pre></figure>
<h2 id="z-index">Z-index</h2>
<p>Several Bootstrap components utilize <code class="highlighter-rouge">z-index</code>, the CSS property that helps control layout by providing a third axis to arrange content. We utilize a default z-index scale in Bootstrap thats been designed to properly layer navigation, tooltips and popovers, modals, and more.</p>
<p>These higher values start at an arbitrary number, high and specific enough to ideally avoid conflicts. We need a standard set of these across our layered components—tooltips, popovers, navbars, dropdowns, modals—so we can be reasonably consistent in the behaviors. Theres no reason we couldnt have used <code class="highlighter-rouge">100</code>+ or <code class="highlighter-rouge">500</code>+.</p>
<p>We dont encourage customization of these individual values; should you change one, you likely need to change them all.</p>
<figure class="highlight"><pre><code class="language-scss" data-lang="scss"><span class="nv">$zindex-dropdown</span><span class="p">:</span> <span class="m">1000</span> <span class="o">!</span><span class="nb">default</span><span class="p">;</span>
<span class="nv">$zindex-sticky</span><span class="p">:</span> <span class="m">1020</span> <span class="o">!</span><span class="nb">default</span><span class="p">;</span>
<span class="nv">$zindex-fixed</span><span class="p">:</span> <span class="m">1030</span> <span class="o">!</span><span class="nb">default</span><span class="p">;</span>
<span class="nv">$zindex-modal-backdrop</span><span class="p">:</span> <span class="m">1040</span> <span class="o">!</span><span class="nb">default</span><span class="p">;</span>
<span class="nv">$zindex-modal</span><span class="p">:</span> <span class="m">1050</span> <span class="o">!</span><span class="nb">default</span><span class="p">;</span>
<span class="nv">$zindex-popover</span><span class="p">:</span> <span class="m">1060</span> <span class="o">!</span><span class="nb">default</span><span class="p">;</span>
<span class="nv">$zindex-tooltip</span><span class="p">:</span> <span class="m">1070</span> <span class="o">!</span><span class="nb">default</span><span class="p">;</span></code></pre></figure>
<p>To handle overlapping borders within components (e.g., buttons and inputs in input groups), we use low single digit <code class="highlighter-rouge">z-index</code> values of <code class="highlighter-rouge">1</code>, <code class="highlighter-rouge">2</code>, and <code class="highlighter-rouge">3</code> for default, hover, and active states. On hover/focus/active, we bring a particular element to the forefront with a higher <code class="highlighter-rouge">z-index</code> value to show their border over the sibling elements.</p>
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