Make modal popup just big enough, with scrollbar if needed - css

Question

Due to reasons beyond my control, we're still using Bootstrap 2.3.2. I have a modal popup that might display anywhere from 1 to 50 lines of information. I made it the maximum size I could to fit on the screen and made the middle part, the .modal-body have a scrollbar if needed. My HTML looks like:
<div id="confirm-popup" class="modal hide fade" role="dialog"
aria-labelledby="confirm-popup-subject" aria-hidden="true">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
<h3 id="confirm-popup-subject">XXX</h3>
</div>
<div class="modal-body" id="confirm-content">
</div>
<div class="modal-footer">
<button id="confirm-popup-edit" class="btn" data-dismiss="modal"
aria-hidden="true">Edit</button>
<button id="confirm-popup-cancel" class="btn" data-dismiss="modal"
aria-hidden="true">Cancel</button>
<button id="confirm-popup-submit" class="btn btn-primary"
aria-hidden="true" data-dismiss="modal">Create Ticket</button>
</div>
</div>
With JavaScript to fill in the $('#confirm-popup-subject') and $('#confirm-content') before popping it up.
I used the following CSS overrides to get this:
#confirm-poup {
top: 2%;
bottom: 2%;
overflow: initial;
}
#confirm-popup .modal-body {
overflow-y: auto;
max-height: 80%;
}
This makes the dialog take up most of the screen, and if it needs a scrollbar it has it. But now the customer is saying that they don't want it to be so big when it only has a few lines of text to display. They want it to be the minimum size it can be and still fit the body text in, but also to still have a scrollbar on the modal-body if the body text won't fit on the screen. Is this possible?

Answer 1

After some experimentation, I got acceptable results if I change the CSS to this:
#confirm-popup {
overflow: initial;
top: 2%;
}
#confirm-popup .modal-body {
overflow-y: auto;
max-height: 70vh;
}
It's not perfect - it overlaps the screen if I make the browser too short - but it works for all supported browser sizes.