If you don’t get an answer here, there are some extremely kind wizards in the #appearance channel of Obsidian’s Discord server who essentially produce snippets on request.
I must be doing something wrong on my end, the change is not taking. If i understand correctly, I create a .css file, with the code you provided, in css snippets?
Yeah, the steps are linked below. The .css file can be named anything. Be sure to use a proper code editor to make it (Notepad++, Sublime Text, VSCode, etc).
Keep in mind, this CSS only covers headings in ![[embeds]], not headings in regular text.
For regular text, you could give these custom properties a try: