description: Shorthand helpers that build on top of our flexbox utilities to make component layout faster and easier than ever.
group: helpers
toc: true
+added: "5.1"
---
Stacks offer a shortcut for applying a number of flexbox properties to quickly and easily create layouts in Bootstrap. All credit for the concept and implementation goes to the open source [Pylon project](https://almonk.github.io/pylon/).
The `opacity` property sets the opacity level for an element. The opacity level describes the transparency level, where `1` is not transparent at all, `.5` is 50% visible, and `0` is completely transparent.