#397E8A

CSS

:root {
  --mysterious-blue: #397e8a;
  --mysterious-blue-rgb: 57 126 138;
  --mysterious-blue-oklch: oklch(0.554 0.071 210.5);
}

.element {
  color: var(--mysterious-blue);
  background-color: hsl(189 42% 38%);
  border-color: oklch(0.554 0.071 210.5);
}

Tailwind CSS v4

@theme {
  --color-mysterious-blue: #397e8a;
  --color-mysterious-blue-50: #dffbff;
  --color-mysterious-blue-100: #ceeff6;
  --color-mysterious-blue-200: #b2dde6;
  --color-mysterious-blue-300: #8dc2cd;
  --color-mysterious-blue-400: #6aaab6;
  --color-mysterious-blue-500: #4693a1;
  --color-mysterious-blue-600: #3c7c88;
  --color-mysterious-blue-700: #30646d;
  --color-mysterious-blue-800: #21494f;
  --color-mysterious-blue-900: #163337;
  --color-mysterious-blue-950: #071e22;
}

SCSS

$mysterious-blue: #397e8a;
$mysterious-blue-rgb: 57, 126, 138;
$mysterious-blue-light: mix(#fff, $mysterious-blue, 20%);
$mysterious-blue-dark: mix(#000, $mysterious-blue, 20%);

.element {
  color: $mysterious-blue;
  box-shadow: 0 0 0 2px rgba($mysterious-blue, 0.35);
}