#3AA5D3

CSS

:root {
  --mystic-blue: #3aa5d3;
  --mystic-blue-rgb: 58 165 211;
  --mystic-blue-oklch: oklch(0.681 0.117 230.7);
}

.element {
  color: var(--mystic-blue);
  background-color: hsl(198 63% 53%);
  border-color: oklch(0.681 0.117 230.7);
}

Tailwind CSS v4

@theme {
  --color-mystic-blue: #3aa5d3;
  --color-mystic-blue-50: #d5fcff;
  --color-mystic-blue-100: #c2efff;
  --color-mystic-blue-200: #a2defe;
  --color-mystic-blue-300: #77c2e9;
  --color-mystic-blue-400: #49abd6;
  --color-mystic-blue-500: #0093c5;
  --color-mystic-blue-600: #007ca6;
  --color-mystic-blue-700: #046385;
  --color-mystic-blue-800: #004962;
  --color-mystic-blue-900: #013345;
  --color-mystic-blue-950: #001e2d;
}

SCSS

$mystic-blue: #3aa5d3;
$mystic-blue-rgb: 58, 165, 211;
$mystic-blue-light: mix(#fff, $mystic-blue, 20%);
$mystic-blue-dark: mix(#000, $mystic-blue, 20%);

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