#5676A3

CSS

:root {
  --montreux-blue: #5676a3;
  --montreux-blue-rgb: 86 118 163;
  --montreux-blue-oklch: oklch(0.56 0.08 257);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(215 31% 49%);
  border-color: oklch(0.56 0.08 257);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5676a3;
  --color-montreux-blue-50: #e8f6ff;
  --color-montreux-blue-100: #d8e9ff;
  --color-montreux-blue-200: #c0d6f7;
  --color-montreux-blue-300: #9fb9e1;
  --color-montreux-blue-400: #80a0cd;
  --color-montreux-blue-500: #6488bb;
  --color-montreux-blue-600: #55739e;
  --color-montreux-blue-700: #445c7e;
  --color-montreux-blue-800: #2f445e;
  --color-montreux-blue-900: #202f42;
  --color-montreux-blue-950: #101b2a;
}

SCSS

$montreux-blue: #5676a3;
$montreux-blue-rgb: 86, 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);
}