That is indeed interesting, will keep that in mind for the future - although I haven’t had any editor performance issues while using margins in my own CSS snippets (except when I & others have used the Minimal theme, which apparently isn’t “minimal” anymore)
Yet I wonder how many Obsidian theme creators know about this and how many of them have used margins in their themes 
Heck, now I understand why certain public CSS snippets make Obsidian choke 
Honestly, that part should really be stated in the Obsidian theme creation docs for all theme creators & CSS snippet writers to be aware of:
P.S. I remember that CSS Flex & Grid layouts don’t suffer from the collapsing margin problem