#5577A0

CSS

:root {
  --montreux-blue: #5577a0;
  --montreux-blue-rgb: 85 119 160;
  --montreux-blue-oklch: oklch(0.56 0.075 253.6);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(213 31% 48%);
  border-color: oklch(0.56 0.075 253.6);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5577a0;
  --color-montreux-blue-50: #e7f7ff;
  --color-montreux-blue-100: #d8eaff;
  --color-montreux-blue-200: #c0d6f5;
  --color-montreux-blue-300: #9ebade;
  --color-montreux-blue-400: #80a1ca;
  --color-montreux-blue-500: #6389b7;
  --color-montreux-blue-600: #54749b;
  --color-montreux-blue-700: #435d7c;
  --color-montreux-blue-800: #2f445c;
  --color-montreux-blue-900: #202f40;
  --color-montreux-blue-950: #0f1b29;
}

SCSS

$montreux-blue: #5577a0;
$montreux-blue-rgb: 85, 119, 160;
$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);
}