How to detect Panel dark mode in CSS?

Panel
1

I have an SVG icon that I’d like to turn dark by using filter: invert(1)

.reaction-icons {
    display: flex;
    align-items: center;
    justify-content: end;
}


:host(.reaction-icons.dark) {
    filter: invert(1);
}

However, I’m not sure what the keys are.