Can't use Boom and Notation themes

Things I have tried

Hi there!

Some community themes are not working for me (Boom and Notation)

I tried several times to start a vault from scratch. Also looked into Github to directly download them, put those css files either in vault root and vault/.obsidian/snippets… but nothing happened.

What I’m trying to do

I just want to try some themes inspired by Notion and Roam. I first tried Arminta’s settings at this link.

Maybe things got messed up after this (I have no CSS knowledge). Anyway, I ended up deleting the entire vault and creating others from the scratch.

I apologize if this is a very basic issue. I looked up for solutions throughout this forum and at Google, but got nothing.

Thank you!