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.
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).
While containers can be nested, most layouts do not require a nested container.
.container-fluid for a full width container, spanning the entire width of the viewport.
Since Bootstrap is developed to be mobile first, we use a handful of 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.
Since we write our source CSS in Sass, all our media queries are available via Sass mixins:
We occasionally use media queries that go in the other direction (the given screen size or smaller):
Once again, these media queries are also available via Sass mixins:
There are also media queries and mixins for targeting a single segment of screen sizes using the minimum and maximum breakpoint widths.
These media queries are also available via Sass mixins:
Similarly, media queries may span multiple breakpoint widths:
The Sass mixin for targeting the same screen size range would be:
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.
We don’t encourage customization of these values; should you change one, you likely need to change them all.
$zindex-dropdown-backdrop: 990 !default; $zindex-dropdown: 1000 !default; $zindex-fixed: 1030 !default; $zindex-sticky: 1030 !default; $zindex-modal-backdrop: 1040 !default; $zindex-modal: 1050 !default; $zindex-popover: 1060 !default; $zindex-tooltip: 1070 !default;
Background elements—like the backdrops that allow click-dismissing—tend to reside on a lower
z-indexs, while navigation and popovers utilize higher
z-indexs to ensure they overlay surrounding content.