#3A808C

CSS

:root {
  --mysterious-blue: #3a808c;
  --mysterious-blue-rgb: 58 128 140;
  --mysterious-blue-oklch: oklch(0.56 0.072 210.3);
}

.element {
  color: var(--mysterious-blue);
  background-color: hsl(189 41% 39%);
  border-color: oklch(0.56 0.072 210.3);
}

Tailwind CSS v4

@theme {
  --color-mysterious-blue: #3a808c;
  --color-mysterious-blue-50: #dffbff;
  --color-mysterious-blue-100: #ceeff6;
  --color-mysterious-blue-200: #b2dde6;
  --color-mysterious-blue-300: #8cc2cd;
  --color-mysterious-blue-400: #69aab6;
  --color-mysterious-blue-500: #4493a1;
  --color-mysterious-blue-600: #3b7d88;
  --color-mysterious-blue-700: #2f646d;
  --color-mysterious-blue-800: #20494f;
  --color-mysterious-blue-900: #153337;
  --color-mysterious-blue-950: #061f22;
}

SCSS

$mysterious-blue: #3a808c;
$mysterious-blue-rgb: 58, 128, 140;
$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);
}