Because Android apps run in a window under ChromeOS, there are small differences in how apps are rendered on Chromebooks. These differences are outlined in the following paragraphs.

## Tasks, windows, and transparency

A[task](https://developer.android.com/guide/components/tasks-and-back-stack)consists of a stack of activities that the user interacts with when running an app. Tasks are presented on ChromeOS as a window with a title bar, with the apps layered on top of each other. Each activity can then be partially translucent, letting the lower layers show through.

In a conventional Android app, the previous task or the desktop shows through beneath the task. In this way, there is always something visible beneath a translucent task.

This does not work in a window environment, for the following reasons:

- The visible content below a window cannot be controlled, and could therefore be anything.
- Fully transparent pixels could "magically" swallow touch or mouse events.
- Window elements might visually be disconnected from the caption, confusing the user with possibly unconnected visual elements.

To mitigate this problem, Play for ChromeOS draws a semitransparent rectangle behind each window. For this reason, apps can never be 100 percent transparent when running under ChromeOS, even when using the`Theme.Translucent.NoTitleBar`theme.