Yeah either s or any space-like character that doesn’t get trimmed. Then if you intend to use those indentations regularly, you can create a userscript that will insert them with a keyboard shortcut.
I have one that insert or wrap my selection with <kbd></kbd> on meta and it’s quite convenient 
On markdown, three spaces get trimmed and four creates a code block, so there are not many options to achieve what your want. Either hacky ways as described, of a custom component/plugin if you have a budget of know how to code that.