Hello there, and thanks for wanting to contribute to Project Forumoji! This style guide exists because even though multiple art styles are nice, we still need a few things for it to actually look like a forum emoji. If your emoji doesn't fit in, it won't look good with the others!
If you still miss a few things, we can still edit your emoji to include the style.
There are multiple things that an emoji has.
If the emoji is pure black, this isn't needed. But all emojis should have an outline, to fit in. Don't worry if it loses some detail! This is pixel art, and that's basically working in the loss of detail.
If the emoji is completely black, then you should coat it in a solid white outline instead. This allows dark mode users to make sense of it!
To make it look like the original smilies, some shading would be nice. We can edit this in easily, so it's fine if it doesn't, but it fits in way nicer.
That's it for now! When you're done, open a pull request with the new emoji(s).