I am pretty sure I installed it correctly using hacs. I see this as a resource
/hacsfiles/lovelace-card-mod/card-mod.js?hacstag=190927524343
I have a card with this yaml
entity: sensor.openweathermap_temperature
name: Temp.
card_mod:
style: |
card-mod {
font-size: 4.0em; /* Adjust as needed */
}
When I adjust the font-size nothing happens
type or paste code here
The code you posted is wrong. Use an example from the card-mod repo.
This the simplest one, colorizing rows in Entities card.
You may find more examples there: main card-mod thread - 1st post - link at the bottom.
Actually, I suggest to ask all card-mod related questions in that thread.
Yet the card-mod (if properly defined) does work and changes may be saved in Editor.
So - do not bother about this error - unless you want to use UI instead of yaml.