The channel list can be collapsed by clicking the icon to the left of the topic. The user list can be collapsed by clicking the icon in the top right corner. Th

The channel list can be collapsed by clicking the icon to the left of the topic. The user list can be collapsed by clicking the icon in the top right corner. There is also an area in the settings to add your own CSS rules. Just wanted to point those things out because they probably aren't immediately visible from the linked page and the screenshot.