#55799F

CSS

:root {
  --montreux-blue: #55799f;
  --montreux-blue-rgb: 85 121 159;
  --montreux-blue-oklch: oklch(0.565 0.072 250.5);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(211 30% 48%);
  border-color: oklch(0.565 0.072 250.5);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #55799f;
  --color-montreux-blue-50: #e7f7ff;
  --color-montreux-blue-100: #d7eaff;
  --color-montreux-blue-200: #bfd7f3;
  --color-montreux-blue-300: #9ebadc;
  --color-montreux-blue-400: #7ea2c8;
  --color-montreux-blue-500: #618ab5;
  --color-montreux-blue-600: #537598;
  --color-montreux-blue-700: #425d7a;
  --color-montreux-blue-800: #2e455a;
  --color-montreux-blue-900: #1f2f3f;
  --color-montreux-blue-950: #0f1c28;
}

SCSS

$montreux-blue: #55799f;
$montreux-blue-rgb: 85, 121, 159;
$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);
}