#5379A2

CSS

:root {
  --montreux-blue: #5379a2;
  --montreux-blue-rgb: 83 121 162;
  --montreux-blue-oklch: oklch(0.565 0.077 251.1);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(211 32% 48%);
  border-color: oklch(0.565 0.077 251.1);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5379a2;
  --color-montreux-blue-50: #e6f7ff;
  --color-montreux-blue-100: #d6eaff;
  --color-montreux-blue-200: #bed7f5;
  --color-montreux-blue-300: #9cbadf;
  --color-montreux-blue-400: #7da2cb;
  --color-montreux-blue-500: #5f8ab8;
  --color-montreux-blue-600: #51759b;
  --color-montreux-blue-700: #405d7d;
  --color-montreux-blue-800: #2d455c;
  --color-montreux-blue-900: #1e2f40;
  --color-montreux-blue-950: #0e1c29;
}

SCSS

$montreux-blue: #5379a2;
$montreux-blue-rgb: 83, 121, 162;
$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);
}