Cool background gradient from https://getbootstrap.com.

cool-bg-color-gradient.css

.foo {
  --color0: 214, 51, 132; /* --bd-pink-rgb */
  --color1: 255, 255, 255; /* --bs-white-rgb */
  --color2: 13, 110, 253; /* --bs-primary-rgb */
  --color3: 255, 228, 132; /* --bd-accent-rgb */
  --color4: 112.520718, 44.062154, 249.437846; /* --bd-violet-rgb */
  background-image: linear-gradient(
      180deg,
      rgba(var(--color1), 0.01),
      rgba(var(--color1), 1) 85%
    ),
    radial-gradient(
      ellipse at top left,
      rgba(var(--color2), 0.5),
      transparent 50%
    ),
    radial-gradient(
      ellipse at top right,
      rgba(var(--color3), 0.5),
      transparent 50%
    ),
    radial-gradient(
      ellipse at center right,
      rgba(var(--color4), 0.5),
      transparent 50%
    ),
    radial-gradient(
      ellipse at center left,
      rgba(var(--color0), 0.5),
      transparent 50%
    );
}