#5A75A6

CSS

:root {
  --montreux-blue: #5a75a6;
  --montreux-blue-rgb: 90 117 166;
  --montreux-blue-oklch: oklch(0.562 0.083 261.9);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(219 30% 50%);
  border-color: oklch(0.562 0.083 261.9);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5a75a6;
  --color-montreux-blue-50: #e9f6ff;
  --color-montreux-blue-100: #dae8ff;
  --color-montreux-blue-200: #c2d5f9;
  --color-montreux-blue-300: #a2b8e3;
  --color-montreux-blue-400: #849fd0;
  --color-montreux-blue-500: #6886bd;
  --color-montreux-blue-600: #5872a0;
  --color-montreux-blue-700: #465b80;
  --color-montreux-blue-800: #31435f;
  --color-montreux-blue-900: #212e43;
  --color-montreux-blue-950: #111b2b;
}

SCSS

$montreux-blue: #5a75a6;
$montreux-blue-rgb: 90, 117, 166;
$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);
}