Place it inside /path/to/obsidian/vault/folder/.obsidian/themes
Activate it by going to the Obsidian Settings menu and on Options -> Appearance -> Themes if you click on the arrows it should appear, select it and there you go
Special thanks to an unkown source for the base theme, I can’t remember where I found it
Troubleshoot
Make sure you placed it on the .obsidian folder that’s INSIDE your vault, not on the one that’s outside
Make sure that the folder that contains the manifest.json and theme.css files has the EXACT (CASE SENSITIVE!!!) name as the one indicated on the manifest.json file otherwise Obsidian will not detect it
