#5479A1

CSS

:root {
  --montreux-blue: #5479a1;
  --montreux-blue-rgb: 84 121 161;
  --montreux-blue-oklch: oklch(0.565 0.075 251.1);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(211 31% 48%);
  border-color: oklch(0.565 0.075 251.1);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5479a1;
  --color-montreux-blue-50: #e7f7ff;
  --color-montreux-blue-100: #d7eaff;
  --color-montreux-blue-200: #bed7f4;
  --color-montreux-blue-300: #9dbade;
  --color-montreux-blue-400: #7da2ca;
  --color-montreux-blue-500: #608ab7;
  --color-montreux-blue-600: #52759a;
  --color-montreux-blue-700: #415d7c;
  --color-montreux-blue-800: #2d455b;
  --color-montreux-blue-900: #1f2f40;
  --color-montreux-blue-950: #0e1c29;
}

SCSS

$montreux-blue: #5479a1;
$montreux-blue-rgb: 84, 121, 161;
$montreux-blue-light: mix(#fff, $montreux-blue, 20%);
$montreux-blue-dark: mix(#000, $montreux-blue, 20%);

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