#425664

CSS

:root {
  --dark-secret: #425664;
  --dark-secret-rgb: 66 86 100;
  --dark-secret-oklch: oklch(0.442 0.034 239);
}

.element {
  color: var(--dark-secret);
  background-color: hsl(205 20% 33%);
  border-color: oklch(0.442 0.034 239);
}

Tailwind CSS v4

@theme {
  --color-dark-secret: #425664;
  --color-dark-secret-50: #edf7fe;
  --color-dark-secret-100: #deeaf2;
  --color-dark-secret-200: #c8d6e2;
  --color-dark-secret-300: #a9bac7;
  --color-dark-secret-400: #8da2b1;
  --color-dark-secret-500: #728a9a;
  --color-dark-secret-600: #617583;
  --color-dark-secret-700: #4d5d69;
  --color-dark-secret-800: #38444d;
  --color-dark-secret-900: #262f35;
  --color-dark-secret-950: #141c20;
}

SCSS

$dark-secret: #425664;
$dark-secret-rgb: 66, 86, 100;
$dark-secret-light: mix(#fff, $dark-secret, 20%);
$dark-secret-dark: mix(#000, $dark-secret, 20%);

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