These are DOM’s in the CSS code, the theme modding is code from ‘card mod’ which you have installed through HACS (otherwise the code I posted wouldn’t have worked on your system)…
thomasloven/lovelace-card-mod: 
Add CSS styles to (almost) any lovelace card (github.com)
It’s very advanced stuff. I’m not an expert myself and still learning CSS. But those signs are basically navigation points inside the CSS code. I linked the Github of card-mod above. You should also visit the card-mod threads for card mods and themes if you want to explore more.
Modding themes 
Card-mod - Super-charge your themes! - Share your Projects! / Themes - Home Assistant Community (home-assistant.io)