#5976A3

CSS

:root {
  --montreux-blue: #5976a3;
  --montreux-blue-rgb: 89 118 163;
  --montreux-blue-oklch: oklch(0.562 0.078 259);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(216 29% 49%);
  border-color: oklch(0.562 0.078 259);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5976a3;
  --color-montreux-blue-50: #e9f6ff;
  --color-montreux-blue-100: #d9e9ff;
  --color-montreux-blue-200: #c2d5f6;
  --color-montreux-blue-300: #a1b8e0;
  --color-montreux-blue-400: #83a0cd;
  --color-montreux-blue-500: #6787ba;
  --color-montreux-blue-600: #57729d;
  --color-montreux-blue-700: #455c7e;
  --color-montreux-blue-800: #31435d;
  --color-montreux-blue-900: #212e41;
  --color-montreux-blue-950: #101b2a;
}

SCSS

$montreux-blue: #5976a3;
$montreux-blue-rgb: 89, 118, 163;
$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);
}