How to add styles to a theme

Configuration Frontend
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1

I’d like to add this style to the theme i am using so to have all the cards with the same style. How to do this?

the style is the following:

card_mod:
  style: |
    ha-card {
    --primary-text-color: #FFFFFF;
    --secondary-text-color: #FFFFFF;
    --divider-color: #FFFFFF;
    --rgb-primary-color: red;
    background-color: rgba(7, 103, 215, 0.4);
    }
2

This should be done by card-mod-theme.
There is a dedicated thread for card-mod-themes, and check examples in GitHub card-mod repo (wiki section for themes, search for “card-mod-card” word)