#5379A5

CSS

:root {
  --montreux-blue: #5379a5;
  --montreux-blue-rgb: 83 121 165;
  --montreux-blue-oklch: oklch(0.566 0.081 252.8);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(212 33% 49%);
  border-color: oklch(0.566 0.081 252.8);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5379a5;
  --color-montreux-blue-50: #e6f7ff;
  --color-montreux-blue-100: #d6eaff;
  --color-montreux-blue-200: #bdd7f7;
  --color-montreux-blue-300: #9cbae1;
  --color-montreux-blue-400: #7ca2ce;
  --color-montreux-blue-500: #5e89bb;
  --color-montreux-blue-600: #50749e;
  --color-montreux-blue-700: #405d7e;
  --color-montreux-blue-800: #2d445e;
  --color-montreux-blue-900: #1e2f42;
  --color-montreux-blue-950: #0e1c2a;
}

SCSS

$montreux-blue: #5379a5;
$montreux-blue-rgb: 83, 121, 165;
$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);
}