Use `z-index` utilities to stack elements on top of one another. Requires a `position` value other than `static`, which can be set with custom styles or using our [position utilities]({{< docsref "/utilities/position/" >}}).
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We call these "low-level" `z-index` utilities because of their default values of `-1` through `3`, which we use for the layout of overlapping components. High-level `z-index` values are used for overlay components like modals and tooltips.
Bootstrap overlay components—dropdown, modal, offcanvas, popover, toast, and tooltip—all have their own `z-index` values to ensure a usable experience with competing "layers" of an interface.
Read about them in the [`z-index` layout page]({{< docsref "/layout/z-index" >}}).
## Component approach
On some components, we use our low-level `z-index` values to manage repeating elements that overlap one another (like buttons in a button group or items in a list group).
Learn about our [`z-index` approach]({{< docsref "/extend/approach#z-index-scales" >}}).
## CSS
### Sass map
Customize this Sass map to change the available values and generated utilities.
Position utilities are declared in our utilities API in `scss/_utilities.scss`. [Learn how to use the utilities API.]({{< docsref "/utilities/api#using-the-api" >}})