#5579A4

CSS

:root {
  --montreux-blue: #5579a4;
  --montreux-blue-rgb: 85 121 164;
  --montreux-blue-oklch: oklch(0.567 0.079 253.5);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(213 32% 49%);
  border-color: oklch(0.567 0.079 253.5);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5579a4;
  --color-montreux-blue-50: #e7f7ff;
  --color-montreux-blue-100: #d7eaff;
  --color-montreux-blue-200: #bed6f6;
  --color-montreux-blue-300: #9dbae0;
  --color-montreux-blue-400: #7ea1cc;
  --color-montreux-blue-500: #6089b9;
  --color-montreux-blue-600: #52749c;
  --color-montreux-blue-700: #415d7e;
  --color-montreux-blue-800: #2e445d;
  --color-montreux-blue-900: #1f2f41;
  --color-montreux-blue-950: #0f1c2a;
}

SCSS

$montreux-blue: #5579a4;
$montreux-blue-rgb: 85, 121, 164;
$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);
}