I hate to be that guy, BUT...

[cssinate]

First let me start by saying as a long-time Slack user, I wish I'd known about this tool years ago. I would have used it a lot more. However, I think you guys should consider archiving the project, and putting a note up on the site that the project is no longer useful. Here are my reasons for that conclusion:

1. Slack no longer uses the same theme format. They use a total of 4 colors now.
2. The colors of the UI seem to get generated by making a bunch of variants of the base colors you put in (see screenshot below). With the complexities of how they update these colors, the combination of the options in the Appearance menu (Dark/Light mode, Window gradient, Darker sidebar (when in light mode and System Navigation color is dark)), it would be way more complicated to accurately replicate the UI
3. Most importantly, the Appearance menu does everything your website does now. As you update colors, they update in real time. And you can copy your theme to your clipboard from right in the Appearance menu.

Now, you might say, "Well, we'll just leave it as is," but the reason I think you should put the message right up on the website is for old-school Slack users like me. I generated a theme, copied the color tokens into Slack and clicked "Apply Slack Theme" and it changed. Then I noticed the hover color wasn't right. So I went back to the website, changed the color to something dramatic to try to debug, copied the new hex codes, and pasted them into Slack. And the button in Slack was disabled. I clicked it anyway and it said "This is already your theme". It took me a while to realize why that was the case, even though I definitely made a change; the color I changed is no longer used by Slack.

It cost me time to debug and figure out what was going on. Whereas, if this information was right on the website, it would have sent me immediately to the Appearance menu, where I could have done all the work on my own there.