#99BAF5

CSS

:root {
  --pastel-blue: #99baf5;
  --pastel-blue-rgb: 153 186 245;
  --pastel-blue-oklch: oklch(0.786 0.092 261.8);
}

.element {
  color: var(--pastel-blue);
  background-color: hsl(218 82% 78%);
  border-color: oklch(0.786 0.092 261.8);
}

Tailwind CSS v4

@theme {
  --color-pastel-blue: #99baf5;
  --color-pastel-blue-50: #e8f6ff;
  --color-pastel-blue-100: #d8e8ff;
  --color-pastel-blue-200: #c0d5fd;
  --color-pastel-blue-300: #9fb8e7;
  --color-pastel-blue-400: #809fd5;
  --color-pastel-blue-500: #6486c3;
  --color-pastel-blue-600: #5571a5;
  --color-pastel-blue-700: #445b84;
  --color-pastel-blue-800: #2f4362;
  --color-pastel-blue-900: #202e45;
  --color-pastel-blue-950: #101b2d;
}

SCSS

$pastel-blue: #99baf5;
$pastel-blue-rgb: 153, 186, 245;
$pastel-blue-light: mix(#fff, $pastel-blue, 20%);
$pastel-blue-dark: mix(#000, $pastel-blue, 20%);

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