#3B7E89

CSS

:root {
  --mysterious-blue: #3b7e89;
  --mysterious-blue-rgb: 59 126 137;
  --mysterious-blue-oklch: oklch(0.554 0.07 209.6);
}

.element {
  color: var(--mysterious-blue);
  background-color: hsl(188 40% 38%);
  border-color: oklch(0.554 0.07 209.6);
}

Tailwind CSS v4

@theme {
  --color-mysterious-blue: #3b7e89;
  --color-mysterious-blue-50: #e0fbff;
  --color-mysterious-blue-100: #ceeff5;
  --color-mysterious-blue-200: #b3dde5;
  --color-mysterious-blue-300: #8ec1cc;
  --color-mysterious-blue-400: #6caab5;
  --color-mysterious-blue-500: #48939f;
  --color-mysterious-blue-600: #3e7c87;
  --color-mysterious-blue-700: #31636c;
  --color-mysterious-blue-800: #22494f;
  --color-mysterious-blue-900: #173337;
  --color-mysterious-blue-950: #071e22;
}

SCSS

$mysterious-blue: #3b7e89;
$mysterious-blue-rgb: 59, 126, 137;
$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);
}