#5A78A5

CSS

:root {
  --montreux-blue: #5a78a5;
  --montreux-blue-rgb: 90 120 165;
  --montreux-blue-oklch: oklch(0.568 0.078 258.3);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(216 29% 50%);
  border-color: oklch(0.568 0.078 258.3);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5a78a5;
  --color-montreux-blue-50: #e8f6ff;
  --color-montreux-blue-100: #d9e9ff;
  --color-montreux-blue-200: #c1d5f7;
  --color-montreux-blue-300: #a1b9e0;
  --color-montreux-blue-400: #82a0cd;
  --color-montreux-blue-500: #6687ba;
  --color-montreux-blue-600: #56739d;
  --color-montreux-blue-700: #455c7e;
  --color-montreux-blue-800: #30435d;
  --color-montreux-blue-900: #212f41;
  --color-montreux-blue-950: #101b2a;
}

SCSS

$montreux-blue: #5a78a5;
$montreux-blue-rgb: 90, 120, 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);
}