UPDATE: Issue fixed with new json theme. However, mattlee there is a problem with the button fill. The fill doesn't actually fill the whole of the last button and is a visual glitch. See the screensh...
Seem like there are related formatting issues from this post with regards to horizontal formatting across the different states of this visual. https://community.fabric.microsoft.com/t5/Issues/New-Button-Slicer-Formatting-Options/idi-p/4674689