#3A6DB3

CSS

:root {
  --matt-blue: #3a6db3;
  --matt-blue-rgb: 58 109 179;
  --matt-blue-oklch: oklch(0.534 0.123 256.8);
}

.element {
  color: var(--matt-blue);
  background-color: hsl(215 51% 46%);
  border-color: oklch(0.534 0.123 256.8);
}

Tailwind CSS v4

@theme {
  --color-matt-blue: #3a6db3;
  --color-matt-blue-50: #e0f7ff;
  --color-matt-blue-100: #cfeaff;
  --color-matt-blue-200: #b5d6ff;
  --color-matt-blue-300: #91b9f7;
  --color-matt-blue-400: #6ea0e6;
  --color-matt-blue-500: #4d87d6;
  --color-matt-blue-600: #4272b5;
  --color-matt-blue-700: #345b91;
  --color-matt-blue-800: #22436c;
  --color-matt-blue-900: #172e4c;
  --color-matt-blue-950: #081b32;
}

SCSS

$matt-blue: #3a6db3;
$matt-blue-rgb: 58, 109, 179;
$matt-blue-light: mix(#fff, $matt-blue, 20%);
$matt-blue-dark: mix(#000, $matt-blue, 20%);

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