#5377A3

CSS

:root {
  --montreux-blue: #5377a3;
  --montreux-blue-rgb: 83 119 163;
  --montreux-blue-oklch: oklch(0.561 0.08 254);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(213 33% 48%);
  border-color: oklch(0.561 0.08 254);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5377a3;
  --color-montreux-blue-50: #e7f7ff;
  --color-montreux-blue-100: #d7eaff;
  --color-montreux-blue-200: #bed6f7;
  --color-montreux-blue-300: #9dbae1;
  --color-montreux-blue-400: #7ea1cd;
  --color-montreux-blue-500: #6089ba;
  --color-montreux-blue-600: #52749d;
  --color-montreux-blue-700: #415d7e;
  --color-montreux-blue-800: #2d445d;
  --color-montreux-blue-900: #1f2f41;
  --color-montreux-blue-950: #0e1b2a;
}

SCSS

$montreux-blue: #5377a3;
$montreux-blue-rgb: 83, 119, 163;
$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);
}