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+---
+layout: docs
+title: Z-index
+description: While not a part of Bootstrap's grid system, z-indexes play an important part in how our components overlay and interact with one another.
+group: layout
+---
+
+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.
+
+{{< scss-docs name="zindex-stack" file="scss/_variables.scss" >}}
+
+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.