#90ADD1

CSS

:root {
  --birdie-num-num: #90add1;
  --birdie-num-num-rgb: 144 173 209;
  --birdie-num-num-oklch: oklch(0.739 0.061 254);
}

.element {
  color: var(--birdie-num-num);
  background-color: hsl(213 41% 69%);
  border-color: oklch(0.739 0.061 254);
}

Tailwind CSS v4

@theme {
  --color-birdie-num-num: #90add1;
  --color-birdie-num-num-50: #eaf6ff;
  --color-birdie-num-num-100: #dbe9fd;
  --color-birdie-num-num-200: #c4d6ef;
  --color-birdie-num-num-300: #a3b9d7;
  --color-birdie-num-num-400: #86a1c3;
  --color-birdie-num-num-500: #6a89af;
  --color-birdie-num-num-600: #5a7493;
  --color-birdie-num-num-700: #485c76;
  --color-birdie-num-num-800: #334457;
  --color-birdie-num-num-900: #232f3d;
  --color-birdie-num-num-950: #121b26;
}

SCSS

$birdie-num-num: #90add1;
$birdie-num-num-rgb: 144, 173, 209;
$birdie-num-num-light: mix(#fff, $birdie-num-num, 20%);
$birdie-num-num-dark: mix(#000, $birdie-num-num, 20%);

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