kosmos.social is now running Mastodon 2.9.0, which comes with a shiny new one-column layout. If you're not a fan of the Tweetdeck-style columns, be sure to check it out! (Also nice with the light-color theme version.)
Just go to preferences and remove the checkmark from "Enable advanced web interface".
Blog post about new layout: https://blog.joinmastodon.org/2019/06/mastodon-2.9/
Release notes: https://github.com/tootsuite/mastodon/releases/tag/v2.9.0
kosmos.social is a friendly place for tooting, run by the Kosmos open-source co-operative.