#5576A3

CSS

:root {
  --montreux-blue: #5576a3;
  --montreux-blue-rgb: 85 118 163;
  --montreux-blue-oklch: oklch(0.56 0.08 256.3);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(215 31% 49%);
  border-color: oklch(0.56 0.08 256.3);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5576a3;
  --color-montreux-blue-50: #e7f6ff;
  --color-montreux-blue-100: #d8e9ff;
  --color-montreux-blue-200: #c0d6f7;
  --color-montreux-blue-300: #9fb9e1;
  --color-montreux-blue-400: #80a1ce;
  --color-montreux-blue-500: #6388bb;
  --color-montreux-blue-600: #54739e;
  --color-montreux-blue-700: #435c7f;
  --color-montreux-blue-800: #2f445e;
  --color-montreux-blue-900: #202f42;
  --color-montreux-blue-950: #0f1b2a;
}

SCSS

$montreux-blue: #5576a3;
$montreux-blue-rgb: 85, 118, 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);
}