The Slacktastic theme for Slack (a chat application); works best with "Clean" message formatting in your personal Slack preferences. This theme by JasWSInc @ WebSharks, Inc.

Slacktastic is all about improving the separation between bot-driven messages & other personal chat messages from your teammates. With Slacktastic it is much easier to find messages from collaborators in a Slack channel; even when there is a lot of other noise. For instance, personal chat messages glow slightly with a white background; bot-driven messages are zoomed out to 80% of their original size. In addition, message attachments get the `overflow-y: scroll` property with a max height of 100px.

NOTE: The design of this theme is quite simple, so it's easy to customize further if you like. There are only a few lines of CSS that enhance the Slack interface. Add additional styles of your own, or tweak the existing styles to your liking :-)