#5975A4

CSS

:root {
  --montreux-blue: #5975a4;
  --montreux-blue-rgb: 89 117 164;
  --montreux-blue-oklch: oklch(0.56 0.08 260.5);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(218 30% 50%);
  border-color: oklch(0.56 0.08 260.5);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5975a4;
  --color-montreux-blue-50: #e9f6ff;
  --color-montreux-blue-100: #dae9ff;
  --color-montreux-blue-200: #c2d5f8;
  --color-montreux-blue-300: #a1b8e1;
  --color-montreux-blue-400: #839fce;
  --color-montreux-blue-500: #6787bc;
  --color-montreux-blue-600: #58729e;
  --color-montreux-blue-700: #465b7f;
  --color-montreux-blue-800: #31435e;
  --color-montreux-blue-900: #212e42;
  --color-montreux-blue-950: #111b2a;
}

SCSS

$montreux-blue: #5975a4;
$montreux-blue-rgb: 89, 117, 164;
$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);
}