There are two ways to achieve this
- use the following theme for activity.
android:theme="@android:style/Theme.Translucent"
- Set background of the activity as a trans parent png image or a transparent code
eg.
android:background="@drawable/transparent_bg"
or
android:background="#33BBFFFF"
this is a semi transparent color
Related Links
How to make a background 20% transparent on Android
Understanding colors on Android (six characters)
- To dismiss activity on tap implement onTouchListener and when touch event is detected call finish();
Hope it helps !!