How to hide/show the content of a div with dynamic hieght?

How to hide/show the content of a div with dynamic hieght?

I am trying to develop a small module (like the collapse component of
twitter bootstrap).
I don't know how to treat the content of the div which is growing up/down,
it could take me many descriptions, nothing's better than an example:
Collapse deployment.
You can see a div.container which is the block destined to grow up/down.
Here i declare height: 50px to illustrate a state of the deployment.
Is there a way to hide the content (here a part of the text) that is out
of the height of a parent div ?
I like the idea that we can access a content only by deploying another
one, but i don't really don't understand how to make it happen properly in
CSS.