Applying a theme is straightforward and is done directly through your Emby Server dashboard.
F12 in your browser..old-class with .new-class in your CSS.If an element refuses to change, try background: black !important; . Use this only as a last resort—it makes future updates even harder. emby css themes upd
If you are looking for more options or specific "Netflix-style" layouts, these are the best places to look: Applying a theme is straightforward and is done