#3B6FA3

CSS

:root {
  --muted-blue: #3b6fa3;
  --muted-blue-rgb: 59 111 163;
  --muted-blue-oklch: oklch(0.53 0.1 250.2);
}

.element {
  color: var(--muted-blue);
  background-color: hsl(210 47% 44%);
  border-color: oklch(0.53 0.1 250.2);
}

Tailwind CSS v4

@theme {
  --color-muted-blue: #3b6fa3;
  --color-muted-blue-50: #e1f8ff;
  --color-muted-blue-100: #d1ebff;
  --color-muted-blue-200: #b6d8fe;
  --color-muted-blue-300: #93bbea;
  --color-muted-blue-400: #70a3d7;
  --color-muted-blue-500: #4f8ac6;
  --color-muted-blue-600: #4475a7;
  --color-muted-blue-700: #365e86;
  --color-muted-blue-800: #244563;
  --color-muted-blue-900: #183046;
  --color-muted-blue-950: #091c2d;
}

SCSS

$muted-blue: #3b6fa3;
$muted-blue-rgb: 59, 111, 163;
$muted-blue-light: mix(#fff, $muted-blue, 20%);
$muted-blue-dark: mix(#000, $muted-blue, 20%);

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