#5379A7

CSS

:root {
  --montreux-blue: #5379a7;
  --montreux-blue-rgb: 83 121 167;
  --montreux-blue-oklch: oklch(0.567 0.084 253.8);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(213 34% 49%);
  border-color: oklch(0.567 0.084 253.8);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5379a7;
  --color-montreux-blue-50: #e6f7ff;
  --color-montreux-blue-100: #d6eaff;
  --color-montreux-blue-200: #bdd6f8;
  --color-montreux-blue-300: #9cbae2;
  --color-montreux-blue-400: #7ca1cf;
  --color-montreux-blue-500: #5e89bd;
  --color-montreux-blue-600: #50749f;
  --color-montreux-blue-700: #405d80;
  --color-montreux-blue-800: #2c445f;
  --color-montreux-blue-900: #1e2f42;
  --color-montreux-blue-950: #0e1b2b;
}

SCSS

$montreux-blue: #5379a7;
$montreux-blue-rgb: 83, 121, 167;
$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);
}