On iPhone/iPad there’s no way to unhide the normally hidden .obsidian where the snippet folder of your vault lives…at least, not from the Files app (as opposed to Mac).
But there are alternative if you want to manipulate your css snippets on iPhone/iPad :
You could use another app … One which can show and access the hidden .obsidian folder, such as Taio (I think) or Textastic (which is paid) … but there could be others