#C1E0EF

CSS

:root {
  --sleepless-blue: #c1e0ef;
  --sleepless-blue-rgb: 193 224 239;
  --sleepless-blue-oklch: oklch(0.889 0.039 228.6);
}

.element {
  color: var(--sleepless-blue);
  background-color: hsl(200 59% 85%);
  border-color: oklch(0.889 0.039 228.6);
}

Tailwind CSS v4

@theme {
  --color-sleepless-blue: #c1e0ef;
  --color-sleepless-blue-50: #ebf7fe;
  --color-sleepless-blue-100: #dcebf3;
  --color-sleepless-blue-200: #c4d8e2;
  --color-sleepless-blue-300: #a4bcc8;
  --color-sleepless-blue-400: #87a3b1;
  --color-sleepless-blue-500: #6c8c9b;
  --color-sleepless-blue-600: #5b7683;
  --color-sleepless-blue-700: #495f69;
  --color-sleepless-blue-800: #34454d;
  --color-sleepless-blue-900: #243035;
  --color-sleepless-blue-950: #121c21;
}

SCSS

$sleepless-blue: #c1e0ef;
$sleepless-blue-rgb: 193, 224, 239;
$sleepless-blue-light: mix(#fff, $sleepless-blue, 20%);
$sleepless-blue-dark: mix(#000, $sleepless-blue, 20%);

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