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+---
+layout: docs
+title: Overview
+description: Components and options for laying out your Bootstrap project, including wrapping containers, a powerful grid system, a flexible media object, and responsive utility classes.
+group: layout
+redirect_from: "/docs/4.5/layout/"
+toc: true
+---
+
+## Containers
+
+Containers are the most basic layout element in Bootstrap and are **required when using our default grid system**. Containers are used to contain, pad, and (sometimes) center the content within them. While containers *can* be nested, most layouts do not require a nested container.
+
+Bootstrap comes with three different containers:
+
+- `.container`, which sets a `max-width` at each responsive breakpoint
+- `.container-fluid`, which is `width: 100%` at all breakpoints
+- `.container-{breakpoint}`, which is `width: 100%` until the specified breakpoint
+
+The table below illustrates how each container's `max-width` compares to the original `.container` and `.container-fluid` across each breakpoint.
+
+See them in action and compare them in our [Grid example]({{ site.baseurl }}/docs/{{ site.docs_version }}/examples/grid/#containers).
+
+<table class="table text-left">
+ <thead>
+ <tr>
+ <th></th>
+ <th>
+ Extra small<br>
+ <span class="font-weight-normal">&lt;576px</span>
+ </th>
+ <th>
+ Small<br>
+ <span class="font-weight-normal">&ge;576px</span>
+ </th>
+ <th>
+ Medium<br>
+ <span class="font-weight-normal">&ge;768px</span>
+ </th>
+ <th>
+ Large<br>
+ <span class="font-weight-normal">&ge;992px</span>
+ </th>
+ <th>
+ Extra large<br>
+ <span class="font-weight-normal">&ge;1200px</span>
+ </th>
+ </tr>
+ </thead>
+ <tbody>
+ <tr>
+ <td><code>.container</code></td>
+ <td class="text-muted">100%</td>
+ <td>540px</td>
+ <td>720px</td>
+ <td>960px</td>
+ <td>1140px</td>
+ </tr>
+ <tr>
+ <td><code>.container-sm</code></td>
+ <td class="text-muted">100%</td>
+ <td>540px</td>
+ <td>720px</td>
+ <td>960px</td>
+ <td>1140px</td>
+ </tr>
+ <tr>
+ <td><code>.container-md</code></td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td>720px</td>
+ <td>960px</td>
+ <td>1140px</td>
+ </tr>
+ <tr>
+ <td><code>.container-lg</code></td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td>960px</td>
+ <td>1140px</td>
+ </tr>
+ <tr>
+ <td><code>.container-xl</code></td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td>1140px</td>
+ </tr>
+ <tr>
+ <td><code>.container-fluid</code></td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ <td class="text-muted">100%</td>
+ </tr>
+ </tbody>
+</table>
+
+### All-in-one
+
+Our default `.container` class is a responsive, fixed-width container, meaning its `max-width` changes at each breakpoint.
+
+{% highlight html %}
+<div class="container">
+ <!-- Content here -->
+</div>
+{% endhighlight %}
+
+### Fluid
+
+Use `.container-fluid` for a full width container, spanning the entire width of the viewport.
+
+{% highlight html %}
+<div class="container-fluid">
+ ...
+</div>
+{% endhighlight %}
+
+### Responsive
+
+Responsive containers are new in Bootstrap v4.4. They allow you to specify a class that is 100% wide until the specified breakpoint is reached, after which we apply `max-width`s for each of the higher breakpoints. For example, `.container-sm` is 100% wide to start until the `sm` breakpoint is reached, where it will scale up with `md`, `lg`, and `xl`.
+
+{% highlight html %}
+<div class="container-sm">100% wide until small breakpoint</div>
+<div class="container-md">100% wide until medium breakpoint</div>
+<div class="container-lg">100% wide until large breakpoint</div>
+<div class="container-xl">100% wide until extra large breakpoint</div>
+{% endhighlight %}
+
+## Responsive breakpoints
+
+Since Bootstrap is developed to be mobile first, we use a handful of [media queries](https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries) 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.
+
+Bootstrap primarily uses the following media query ranges—or breakpoints—in our source Sass files for our layout, grid system, and components.
+
+{% highlight scss %}
+// Extra small devices (portrait phones, less than 576px)
+// No media query for `xs` since this is the default in Bootstrap
+
+// Small devices (landscape phones, 576px and up)
+@media (min-width: 576px) { ... }
+
+// Medium devices (tablets, 768px and up)
+@media (min-width: 768px) { ... }
+
+// Large devices (desktops, 992px and up)
+@media (min-width: 992px) { ... }
+
+// Extra large devices (large desktops, 1200px and up)
+@media (min-width: 1200px) { ... }
+{% endhighlight %}
+
+Since we write our source CSS in Sass, all our media queries are available via Sass mixins:
+
+{% highlight scss %}
+// No media query necessary for xs breakpoint as it's effectively `@media (min-width: 0) { ... }`
+@include media-breakpoint-up(sm) { ... }
+@include media-breakpoint-up(md) { ... }
+@include media-breakpoint-up(lg) { ... }
+@include media-breakpoint-up(xl) { ... }
+
+// Example: Hide starting at `min-width: 0`, and then show at the `sm` breakpoint
+.custom-class {
+ display: none;
+}
+@include media-breakpoint-up(sm) {
+ .custom-class {
+ display: block;
+ }
+}
+{% endhighlight %}
+
+We occasionally use media queries that go in the other direction (the given screen size *or smaller*):
+
+{% highlight scss %}
+// Extra small devices (portrait phones, less than 576px)
+@media (max-width: 575.98px) { ... }
+
+// Small devices (landscape phones, less than 768px)
+@media (max-width: 767.98px) { ... }
+
+// Medium devices (tablets, less than 992px)
+@media (max-width: 991.98px) { ... }
+
+// Large devices (desktops, less than 1200px)
+@media (max-width: 1199.98px) { ... }
+
+// Extra large devices (large desktops)
+// No media query since the extra-large breakpoint has no upper bound on its width
+{% endhighlight %}
+
+{% include callout-info-mediaqueries-breakpoints.md %}
+
+Once again, these media queries are also available via Sass mixins:
+
+{% highlight scss %}
+@include media-breakpoint-down(xs) { ... }
+@include media-breakpoint-down(sm) { ... }
+@include media-breakpoint-down(md) { ... }
+@include media-breakpoint-down(lg) { ... }
+// No media query necessary for xl breakpoint as it has no upper bound on its width
+
+// Example: Style from medium breakpoint and down
+@include media-breakpoint-down(md) {
+ .custom-class {
+ display: block;
+ }
+}
+{% endhighlight %}
+
+There are also media queries and mixins for targeting a single segment of screen sizes using the minimum and maximum breakpoint widths.
+
+{% highlight scss %}
+// Extra small devices (portrait phones, less than 576px)
+@media (max-width: 575.98px) { ... }
+
+// Small devices (landscape phones, 576px and up)
+@media (min-width: 576px) and (max-width: 767.98px) { ... }
+
+// Medium devices (tablets, 768px and up)
+@media (min-width: 768px) and (max-width: 991.98px) { ... }
+
+// Large devices (desktops, 992px and up)
+@media (min-width: 992px) and (max-width: 1199.98px) { ... }
+
+// Extra large devices (large desktops, 1200px and up)
+@media (min-width: 1200px) { ... }
+{% endhighlight %}
+
+These media queries are also available via Sass mixins:
+
+{% highlight scss %}
+@include media-breakpoint-only(xs) { ... }
+@include media-breakpoint-only(sm) { ... }
+@include media-breakpoint-only(md) { ... }
+@include media-breakpoint-only(lg) { ... }
+@include media-breakpoint-only(xl) { ... }
+{% endhighlight %}
+
+Similarly, media queries may span multiple breakpoint widths:
+
+{% highlight scss %}
+// Example
+// Apply styles starting from medium devices and up to extra large devices
+@media (min-width: 768px) and (max-width: 1199.98px) { ... }
+{% endhighlight %}
+
+The Sass mixin for targeting the same screen size range would be:
+
+{% highlight scss %}
+@include media-breakpoint-between(md, xl) { ... }
+{% endhighlight %}
+
+## Z-index
+
+Several Bootstrap components utilize `z-index`, the CSS property that helps control layout by providing a third axis to arrange content. We utilize a default z-index scale in Bootstrap that's been designed to properly layer navigation, tooltips and popovers, modals, and more.
+
+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. There's no reason we couldn't have used `100`+ or `500`+.
+
+We don't encourage customization of these individual values; should you change one, you likely need to change them all.
+
+{% highlight scss %}
+$zindex-dropdown: 1000 !default;
+$zindex-sticky: 1020 !default;
+$zindex-fixed: 1030 !default;
+$zindex-modal-backdrop: 1040 !default;
+$zindex-modal: 1050 !default;
+$zindex-popover: 1060 !default;
+$zindex-tooltip: 1070 !default;
+{% endhighlight %}
+
+To handle overlapping borders within components (e.g., buttons and inputs in input groups), we use low single digit `z-index` values of `1`, `2`, and `3` for default, hover, and active states. On hover/focus/active, we bring a particular element to the forefront with a higher `z-index` value to show their border over the sibling elements.