The thread’s title “template in mini-graph-card” is wrong, you admitted yourself that this a stack card’s title.
A possible solution could be using a standard Markdown card placed in a vertical stack with your horizontal stack. Markdown supports templates and may be styled (font size) to mimic a card’s title.
First : I modified the title of my post, to be clearer.
Then, as I come from Domoticz and am a total beginner in HA, I carefully read your messages and tried to make all the pieces match.
Thanks to you, I think I now understand what is a card, how to mix them and what are markdown cards. I’m still struggling to perfectly understand how to write templates, but I hope to be in the right direction.
And you are right in your approach of using i.e nested-stacks , i.e a vertical for the entities/cards “belonging to each other” , then you can have horizontal/vertical stacks/cards inside the initial vertical stack etc.