#5879A1

CSS

:root {
  --montreux-blue: #5879a1;
  --montreux-blue-rgb: 88 121 161;
  --montreux-blue-oklch: oklch(0.567 0.073 253.7);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(213 29% 49%);
  border-color: oklch(0.567 0.073 253.7);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5879a1;
  --color-montreux-blue-50: #e8f7ff;
  --color-montreux-blue-100: #d8eaff;
  --color-montreux-blue-200: #c0d6f4;
  --color-montreux-blue-300: #9fbadd;
  --color-montreux-blue-400: #80a1c9;
  --color-montreux-blue-500: #6489b6;
  --color-montreux-blue-600: #55749a;
  --color-montreux-blue-700: #445d7b;
  --color-montreux-blue-800: #2f445b;
  --color-montreux-blue-900: #202f40;
  --color-montreux-blue-950: #101b29;
}

SCSS

$montreux-blue: #5879a1;
$montreux-blue-rgb: 88, 121, 161;
$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);
}