src/scss/bootstrap-4.0.0-alpha.6/docs/layout/overview.md

   1 ---
   2 layout: docs
   3 title: Overview
   4 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.
   5 group: layout
   6 redirect_from: "/layout/"
   7 ---
   8
   9 Bootstrap includes several components and options for laying out your project, including wrapping containers, a powerful flexbox grid system, a flexible media object, and responsive utility classes.
  10
  11 ## Contents
  12
  13 * Will be replaced with the ToC, excluding the "Contents" header
  14 {:toc}
  15
  16 ## Containers
  17
  18 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).
  19
  20 While containers *can* be nested, most layouts do not require a nested container.
  21
  22 <div class="bd-example">
  23   <div class="bd-example-container">
  24     <div class="bd-example-container-header"></div>
  25     <div class="bd-example-container-sidebar"></div>
  26     <div class="bd-example-container-body"></div>
  27   </div>
  28 </div>
  29
  30 {% highlight html %}
  31 <div class="container">
  32   <!-- Content here -->
  33 </div>
  34 {% endhighlight %}
  35
  36 Use `.container-fluid` for a full width container, spanning the entire width of the viewport.
  37
  38 <div class="bd-example">
  39   <div class="bd-example-container bd-example-container-fluid">
  40     <div class="bd-example-container-header"></div>
  41     <div class="bd-example-container-sidebar"></div>
  42     <div class="bd-example-container-body"></div>
  43   </div>
  44 </div>
  45
  46 {% highlight html %}
  47 <div class="container-fluid">
  48   ...
  49 </div>
  50 {% endhighlight %}
  51
  52
  53 ## Responsive breakpoints
  54
  55 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.
  56
  57 Bootstrap primarily uses the following media query ranges—or breakpoints—in our source Sass files for our layout, grid system, and components.
  58
  59 {% highlight scss %}
  60 // Extra small devices (portrait phones, less than 576px)
  61 // No media query since this is the default in Bootstrap
  62
  63 // Small devices (landscape phones, 576px and up)
  64 @media (min-width: 576px) { ... }
  65
  66 // Medium devices (tablets, 768px and up)
  67 @media (min-width: 768px) { ... }
  68
  69 // Large devices (desktops, 992px and up)
  70 @media (min-width: 992px) { ... }
  71
  72 // Extra large devices (large desktops, 1200px and up)
  73 @media (min-width: 1200px) { ... }
  74 {% endhighlight %}
  75
  76 Since we write our source CSS in Sass, all our media queries are available via Sass mixins:
  77
  78 {% highlight scss %}
  79 @include media-breakpoint-up(xs) { ... }
  80 @include media-breakpoint-up(sm) { ... }
  81 @include media-breakpoint-up(md) { ... }
  82 @include media-breakpoint-up(lg) { ... }
  83 @include media-breakpoint-up(xl) { ... }
  84
  85 // Example usage:
  86 @include media-breakpoint-up(sm) {
  87   .some-class {
  88     display: block;
  89   }
  90 }
  91 {% endhighlight %}
  92
  93 We occasionally use media queries that go in the other direction (the given screen size *or smaller*):
  94
  95 {% highlight scss %}
  96 // Extra small devices (portrait phones, less than 576px)
  97 @media (max-width: 575px) { ... }
  98
  99 // Small devices (landscape phones, less than 768px)
 100 @media (max-width: 767px) { ... }
 101
 102 // Medium devices (tablets, less than 992px)
 103 @media (max-width: 991px) { ... }
 104
 105 // Large devices (desktops, less than 1200px)
 106 @media (max-width: 1199px) { ... }
 107
 108 // Extra large devices (large desktops)
 109 // No media query since the extra-large breakpoint has no upper bound on its width
 110 {% endhighlight %}
 111
 112 Once again, these media queries are also available via Sass mixins:
 113
 114 {% highlight scss %}
 115 @include media-breakpoint-down(xs) { ... }
 116 @include media-breakpoint-down(sm) { ... }
 117 @include media-breakpoint-down(md) { ... }
 118 @include media-breakpoint-down(lg) { ... }
 119 {% endhighlight %}
 120
 121 There are also media queries and mixins for targeting a single segment of screen sizes using the minimum and maximum breakpoint widths.
 122
 123 {% highlight scss %}
 124 // Extra small devices (portrait phones, less than 576px)
 125 @media (max-width: 575px) { ... }
 126
 127 // Small devices (landscape phones, 576px and up)
 128 @media (min-width: 576px) and (max-width: 767px) { ... }
 129
 130 // Medium devices (tablets, 768px and up)
 131 @media (min-width: 768px) and (max-width: 991px) { ... }
 132
 133 // Large devices (desktops, 992px and up)
 134 @media (min-width: 992px) and (max-width: 1199px) { ... }
 135
 136 // Extra large devices (large desktops, 1200px and up)
 137 @media (min-width: 1200px) { ... }
 138 {% endhighlight %}
 139
 140 These media queries are also available via Sass mixins:
 141
 142 {% highlight scss %}
 143 @include media-breakpoint-only(xs) { ... }
 144 @include media-breakpoint-only(sm) { ... }
 145 @include media-breakpoint-only(md) { ... }
 146 @include media-breakpoint-only(lg) { ... }
 147 @include media-breakpoint-only(xl) { ... }
 148 {% endhighlight %}
 149
 150 Similarly, media queries may span multiple breakpoint widths:
 151
 152 {% highlight scss %}
 153 // Example
 154 // Apply styles starting from medium devices and up to extra large devices
 155 @media (min-width: 768px) and (max-width: 1199px) { ... }
 156 {% endhighlight %}
 157
 158 The Sass mixin for targeting the same screen size range would be:
 159
 160 {% highlight scss %}
 161 @include media-breakpoint-between(md, xl) { ... }
 162 {% endhighlight %}
 163
 164 ## Z-index
 165
 166 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.
 167
 168 We don't encourage customization of these values; should you change one, you likely need to change them all.
 169
 170 ```scss
 171 $zindex-dropdown-backdrop:  990 !default;
 172 $zindex-navbar:            1000 !default;
 173 $zindex-dropdown:          1000 !default;
 174 $zindex-fixed:             1030 !default;
 175 $zindex-sticky:            1030 !default;
 176 $zindex-modal-backdrop:    1040 !default;
 177 $zindex-modal:             1050 !default;
 178 $zindex-popover:           1060 !default;
 179 $zindex-tooltip:           1070 !default;
 180 ```
 181
 182 Background elements—like the backdrops that allow click-dismissing—tend to reside on a lower `z-index`s, while navigation and popovers utilize higher `z-index`s to ensure they overlay surrounding content.