#5B75A5

CSS

:root {
  --montreux-blue: #5b75a5;
  --montreux-blue-rgb: 91 117 165;
  --montreux-blue-oklch: oklch(0.562 0.081 262.2);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(219 29% 50%);
  border-color: oklch(0.562 0.081 262.2);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5b75a5;
  --color-montreux-blue-50: #eaf6ff;
  --color-montreux-blue-100: #dae8ff;
  --color-montreux-blue-200: #c3d5f8;
  --color-montreux-blue-300: #a3b8e2;
  --color-montreux-blue-400: #859fcf;
  --color-montreux-blue-500: #6986bc;
  --color-montreux-blue-600: #59729f;
  --color-montreux-blue-700: #475b80;
  --color-montreux-blue-800: #32435f;
  --color-montreux-blue-900: #222e42;
  --color-montreux-blue-950: #111b2b;
}

SCSS

$montreux-blue: #5b75a5;
$montreux-blue-rgb: 91, 117, 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);
}