PivotCX dynamically optimizes the size of the chat window depending on the screen size someone is using. Sometimes, however, some elements in the window can appear too big making it difficult to view the chat log.
If the delivery window or the message input area is getting too big and taking up the majority of the window, the best solution is to hit command+minus/control+minus to zoom out your browser which will resize the window to make the chat visible. Hitting command+plus/control+plus will zoom back in and command+0/control+0 will reset the zoom to default. Zoom settings are also available in most browsers' settings.