The scrollbar is missing on default 100% height

Problem/Motivation

The new toolbar chatbot on Gin in Drupal CMS 1.1, when set with the default 100% height, hides the chatbox behind an overflow and is not scrollabar if the messages is long enough. See screenshot:

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When setting a px height, it works.

Steps to reproduce (required for bugs, but not feature requests)

* Gin & DCMS 1.1.
* Update a block to style Toolbar, region Toolbar
* Write a lot.

Proposed resolution

Either set a better default or fix so that the scrollbar shows up on 100% height.