I am Adam from the Neonto team. I apologize for the delay, we had a little discussion internally about your question.
I think the first and most important thing to say is this: React Studio is a complex, feature-rich program that takes time to learn. It might be deceptively easy to get started with, but it is comparable to Photoshop in terms of the time it takes to learn how to use it to full effect, especially to master the use of key lines and the positioning controls in the layout tab. This is likely the cause of your misalignments. I would be happy to look that over with you to see if I can fix the issues.
The second most important thing to say is that our in-studio mini-previews are not substitutes for full previews in a browser. We are currently discussing ways in which to make this more clear to new users. Below is one of the ideas we are considering, users can switch between the three different styles; we would love to know what you think about this.
As part of this revision, we will make it easier for you to control the final look in the browser using conventional CSS. This will solve your button color and font size problems.
The third thing is: the immediate fix for the buttons and fonts is to identify the appropriate selector (I can help you do this if you do not know how) and write some css that fixes your issues, and then to append it to ~/Documents/React\ Studio/Exported\ Projects\YOURAPPLICATIONNAMEHERE\src\App.css. We regret you having to do this workaround, it will not be for too long before we get out our update.
Adam and the Neonto Team