#0F2B30

CSS

:root {
  --black-box: #0f2b30;
  --black-box-rgb: 15 43 48;
  --black-box-oklch: oklch(0.27 0.035 210.9);
}

.element {
  color: var(--black-box);
  background-color: hsl(189 52% 12%);
  border-color: oklch(0.27 0.035 210.9);
}

Tailwind CSS v4

@theme {
  --color-black-box: #0f2b30;
  --color-black-box-50: #ebf8fb;
  --color-black-box-100: #dcebef;
  --color-black-box-200: #c4d8dd;
  --color-black-box-300: #a4bcc2;
  --color-black-box-400: #88a4aa;
  --color-black-box-500: #6c8d93;
  --color-black-box-600: #5b777d;
  --color-black-box-700: #495f64;
  --color-black-box-800: #354649;
  --color-black-box-900: #243032;
  --color-black-box-950: #131d1e;
}

SCSS

$black-box: #0f2b30;
$black-box-rgb: 15, 43, 48;
$black-box-light: mix(#fff, $black-box, 20%);
$black-box-dark: mix(#000, $black-box, 20%);

.element {
  color: $black-box;
  box-shadow: 0 0 0 2px rgba($black-box, 0.35);
}