complex.css

:root {
	--dark-mode: false;
	--fancy-mode: false;
}

@media screen and (prefers-color-scheme: dark) {
	:root {
		--dark-mode: true;
	}
}

.dark-mode {
	--dark-mode: true;
}

.dark-node.no-js {
	--dark-mode: false;
}

.fancy-mode {
	--fancy-mode: true;
}

.fancy-node.no-js {
	--fancy-mode: false;
}

.something {
	color: csstools-if(--dark-mode black else white);
	background-color: csstools-if(--dark-mode yellow else brown);
	background-color: csstools-if(--dark-mode cyan else blue);
}

.something-else {
	text-decoration: underline csstools-if(--fancy-mode wavy else solid) 1px red;
}

.nested {
	color: csstools-if(--dark-mode red else csstools-if(--fancy-mode orange else yellow));
	background-color: csstools-if(--dark-mode csstools-if(--fancy-mode rgb(0, 123, 255) else rgb(0, 255, 174)) else rgb(255, 0, 200));
}