body {
    min-height: 100vh;

/*    background-image: linear-gradient(
        135deg,
        rgb(0, 255, 0),
        rgb(255, 0, 255)
    );



    background-repeat: no-repeat;
    background-attachment: fixed;
*/
}
body {
  margin: 0;
  min-height: 100vh;
  background: linear-gradient(
    135deg,
    green,
    yellow,
    violet,
    indigo,
    orange,
    red,
    blue
  
    );
  background-size: 400% 400%;
  animation: rainbow 10s ease infinite;
}

@keyframes rainbow {
  0%   { background-position: 0% 50%; }
  50%  { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}
.center {
  display: block;
  margin-left: auto;
  margin-right: auto;
}