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192 lines
6.9 KiB
Markdown
192 lines
6.9 KiB
Markdown
---
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layout: docs
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title: Overview
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description: Components and options for laying out your Bootstrap project, including wrapping containers, a powerful grid system, and responsive utility classes.
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group: layout
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aliases: "/docs/4.3/layout/"
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toc: true
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---
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## Containers
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Containers are the most basic layout element in Bootstrap and are **required when using our default grid system**. Choose from a responsive, fixed-width container (meaning its `max-width` changes at each breakpoint) or fluid-width (meaning it's `100%` wide all the time).
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While containers *can* be nested, most layouts do not require a nested container.
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<div class="bd-example">
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<div class="bd-example-container">
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<div class="bd-example-container-header"></div>
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<div class="bd-example-container-sidebar"></div>
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<div class="bd-example-container-body"></div>
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</div>
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</div>
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{{< highlight html >}}
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<div class="container">
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<!-- Content here -->
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</div>
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{{< /highlight >}}
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Use `.container-fluid` for a full width container, spanning the entire width of the viewport.
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<div class="bd-example">
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<div class="bd-example-container bd-example-container-fluid">
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<div class="bd-example-container-header"></div>
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<div class="bd-example-container-sidebar"></div>
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<div class="bd-example-container-body"></div>
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</div>
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</div>
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{{< highlight html >}}
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<div class="container-fluid">
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...
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</div>
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{{< /highlight >}}
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## Responsive breakpoints
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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.
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Bootstrap primarily uses the following media query ranges—or breakpoints—in our source Sass files for our layout, grid system, and components.
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{{< highlight scss >}}
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// Extra small devices (portrait phones, less than 576px)
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// No media query for `xs` since this is the default in Bootstrap
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// Small devices (landscape phones, 576px and up)
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@media (min-width: 576px) { ... }
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// Medium devices (tablets, 768px and up)
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@media (min-width: 768px) { ... }
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// Large devices (desktops, 992px and up)
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@media (min-width: 992px) { ... }
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// Extra large devices (large desktops, 1200px and up)
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@media (min-width: 1200px) { ... }
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{{< /highlight >}}
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Since we write our source CSS in Sass, all our media queries are available via Sass mixins:
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{{< highlight scss >}}
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// No media query necessary for xs breakpoint as it's effectively `@media (min-width: 0) { ... }`
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@include media-breakpoint-up(sm) { ... }
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@include media-breakpoint-up(md) { ... }
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@include media-breakpoint-up(lg) { ... }
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@include media-breakpoint-up(xl) { ... }
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// Example: Hide starting at `min-width: 0`, and then show at the `sm` breakpoint
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.custom-class {
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display: none;
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}
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@include media-breakpoint-up(sm) {
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.custom-class {
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display: block;
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}
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}
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{{< /highlight >}}
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We occasionally use media queries that go in the other direction (the given screen size *or smaller*):
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{{< highlight scss >}}
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// Extra small devices (portrait phones, less than 576px)
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@media (max-width: 575.98px) { ... }
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// Small devices (landscape phones, less than 768px)
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@media (max-width: 767.98px) { ... }
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// Medium devices (tablets, less than 992px)
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@media (max-width: 991.98px) { ... }
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// Large devices (desktops, less than 1200px)
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@media (max-width: 1199.98px) { ... }
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// Extra large devices (large desktops)
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// No media query since the extra-large breakpoint has no upper bound on its width
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{{< /highlight >}}
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{{< callout info >}}
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{{< partial "callout-info-mediaqueries-breakpoints.md" >}}
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{{< /callout >}}
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Once again, these media queries are also available via Sass mixins:
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{{< highlight scss >}}
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@include media-breakpoint-down(xs) { ... }
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@include media-breakpoint-down(sm) { ... }
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@include media-breakpoint-down(md) { ... }
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@include media-breakpoint-down(lg) { ... }
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// No media query necessary for xl breakpoint as it has no upper bound on its width
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// Example: Style from medium breakpoint and down
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@include media-breakpoint-down(md) {
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.custom-class {
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display: block;
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}
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}
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{{< /highlight >}}
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There are also media queries and mixins for targeting a single segment of screen sizes using the minimum and maximum breakpoint widths.
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{{< highlight scss >}}
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// Extra small devices (portrait phones, less than 576px)
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@media (max-width: 575.98px) { ... }
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// Small devices (landscape phones, 576px and up)
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@media (min-width: 576px) and (max-width: 767.98px) { ... }
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// Medium devices (tablets, 768px and up)
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@media (min-width: 768px) and (max-width: 991.98px) { ... }
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// Large devices (desktops, 992px and up)
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@media (min-width: 992px) and (max-width: 1199.98px) { ... }
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// Extra large devices (large desktops, 1200px and up)
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@media (min-width: 1200px) { ... }
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{{< /highlight >}}
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These media queries are also available via Sass mixins:
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{{< highlight scss >}}
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@include media-breakpoint-only(xs) { ... }
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@include media-breakpoint-only(sm) { ... }
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@include media-breakpoint-only(md) { ... }
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@include media-breakpoint-only(lg) { ... }
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@include media-breakpoint-only(xl) { ... }
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{{< /highlight >}}
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Similarly, media queries may span multiple breakpoint widths:
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{{< highlight scss >}}
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// Example
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// Apply styles starting from medium devices and up to extra large devices
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@media (min-width: 768px) and (max-width: 1199.98px) { ... }
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{{< /highlight >}}
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The Sass mixin for targeting the same screen size range would be:
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{{< highlight scss >}}
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@include media-breakpoint-between(md, xl) { ... }
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{{< /highlight >}}
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## Z-index
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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.
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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`+.
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We don't encourage customization of these individual values; should you change one, you likely need to change them all.
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{{< highlight scss >}}
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$zindex-dropdown: 1000 !default;
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$zindex-sticky: 1020 !default;
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$zindex-fixed: 1030 !default;
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$zindex-modal-backdrop: 1040 !default;
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$zindex-modal: 1050 !default;
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$zindex-popover: 1060 !default;
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$zindex-tooltip: 1070 !default;
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{{< /highlight >}}
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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.
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