Relative Color

.lighten-by-25 {
  background: oklch(from blue calc(l * 1.25) c h);
  background: oklch(from blue calc(l + .25) c h);
}

.lighten-to-75 {
  background: oklch(from blue 75% c h);
}

.set-alpha {
  background: hsl(from blue h s l / 50%);
  background: oklch(from blue l c h / 50%);
  background: rgb(from blue r g b / 50%);
}

.complementary-color {
  background: hsl(from blue calc(h + 180) s l);
}