Automatic foreground color contrast based on the provided background color.
button {
--background: black;
--foreground: color(
from var(--background) xyz round(up, min(1, max(0, 0.18 - y)))
round(up, min(1, max(0, 0.18 - y))) round(up, min(1, max(0, 0.18 - y)))
);
background-color: var(--background);
color: var(--foreground);
}