Slack for Desktop now supports a built-in dark mode
It's been years in the making, but Slack today has suddenly announced and implemented support for dark mode for all users on desktop.
Though dark mode has been available on the mobile versions of Slack since the middle of June, many have waited with baited breath for the same functionality to launch across Slack's desktop form factor. According to the official blog post announcing the feature, implementing support for dark mode in Slack involved "re-architecting the client, building design systems and a dash of derring-do." The specifics of these challenges are described in a separate engineering blog post that showcases how the development team centralized development standards to accommodate the exponential growth of both its user and employee bases.
In addition to dark mode being usable across both desktop and mobile, Slack will also soon launch a “sync with OS settings” feature that allows you to set your theme preferences across both desktop and mobile form factors. In the meantime, the theme you choose for Slack does not reflect across both desktop and mobile form factors automatically.
In order to access dark mode on Slack, you need to be running version 4.0.2 on Windows and Linux, and version 4.0.3 on macOS. If Slack is constantly running on your machines, refreshing once or twice should do the trick for ensuring the option shows up. Once you're certain you've met all of the requirements, the option to enable dark mode should be available by clicking on your name on the left sidebar (or going into the "File" submenu), selecting Preferences, and then choosing the Themes category.
The Official Slack Blog post