#3D4F5F

CSS

:root {
  --dark-secret: #3d4f5f;
  --dark-secret-rgb: 61 79 95;
  --dark-secret-oklch: oklch(0.419 0.035 245.6);
}

.element {
  color: var(--dark-secret);
  background-color: hsl(208 22% 31%);
  border-color: oklch(0.419 0.035 245.6);
}

Tailwind CSS v4

@theme {
  --color-dark-secret: #3d4f5f;
  --color-dark-secret-50: #eef6ff;
  --color-dark-secret-100: #dfe9f3;
  --color-dark-secret-200: #c9d6e3;
  --color-dark-secret-300: #aab9c9;
  --color-dark-secret-400: #8ea1b2;
  --color-dark-secret-500: #73899c;
  --color-dark-secret-600: #627484;
  --color-dark-secret-700: #4e5d6a;
  --color-dark-secret-800: #38444e;
  --color-dark-secret-900: #262f36;
  --color-dark-secret-950: #151b21;
}

SCSS

$dark-secret: #3d4f5f;
$dark-secret-rgb: 61, 79, 95;
$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);
}