Resolve #218, Add One Monokai Darker theme

[brandonreid]

No description provided.

[tplk]

Maybe it'd be better to split the fix and addition of the new theme into two separate PRs?

[mastermel]

Please only commit changes to files in the scss/ directory. For more information please see the contributing guide. Thanks! :)

[tplk]

@mastermel shouldn't you rebuild css from sources before commiting?
I think that's what has been done here.

[mastermel]

I believe @laCour set up this project with the intention that the css/ files be built and committed by just a few people in order to prevent conflicts. So far I think he's the only one that's done that after new changes have been merged for the scss/ directory. I could be mistaken though 😊

You'll notice this current PR is now conflicted with master because of this exact thing. Also, this part of the contributing guide is what I'm basing off of: https://github.com/laCour/slack-night-mode/blob/master/CONTRIBUTING.md#syncing-with-upstream

[vfede]

#218 is now fixed by 515cdc3