Describe the bug
The chat is not positioned correctly in the horizontal direction on screens under 575.98px width.
It seems to be offset to the left by 3em for the MUC chat and 2em for the single conversation and controlbox.

To Reproduce
Steps to reproduce the behavior:

1. Initialize Converse.js in "overlayed" mode
2. Resize the browser to under 575.98px or open the page on the mobile device

Expected behavior
The flyout box should be correctly positioned in the middle of the screen and should horizontally stretch to each side

Screenshots

Environment (please complete the following information):

• Mobile
• Chrome
• Converse.js version 11