Call to Actions (Submit, New Suggestion)
The UI is very clean and I prefer it to some other programs. However, there is one thing that does seem to be more of a design over function issue and that's the call to actions (CTAs) like the submit button and the new suggestion button.
The "Submit" and "New Suggestion" buttons don't seem like buttons and look more like a search field. I had a difficult time finding it and so did a colleague of mine. Considering that sleekplan is definitely sleek and there aren't many elements on the page to start with, it does work against gathering feedback if user's are unsure of how to submit a feedback or suggestion.
I'm not a UI expert by any means, but I can say that it did make it a little harder to navigate the platform. Maybe fill the button color and make it customizable so it can fit with people's themes?