Purpose has a handful of media queries to create sensible breakpoints for our layouts and interfaces.
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.
Use .container-fluid for a full width container, spanning the entire width of the viewport.
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.
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.
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: