animated background

index.html

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title>Animated Background</title>
  <meta name="robots" content="noindex, nofollow">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="styles.css">
</head>

<body>
  <header>
    <h1>Animated Background</h1>
  </header>
  <div class="wrapper">
    <div class="container">
      <h2>Heading</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Cum quibusdam ea atque cumque neque distinctio officia, similique saepe consequuntur, dignissimos officiis aspernatur totam non itaque! Natus voluptatem quasi nostrum doloribus.
      </p>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Dolorum, commodi voluptatibus eligendi. Quam velit repellat minus, sit necessitatibus ad laborum aperiam eaque exercitationem quae vel architecto ex laboriosam nihil modi.</p>
    </div>
    <!-- .container-->
  </div>
  <!-- .wrapper-->
  <footer>
    <small><a href="https://opensource.org/licenses/MIT">MIT</a></small>
  </footer>
</body>

</html>

styles.css

body {
  background:#eeeeee;
  font-size: 16px;
  font-family: "Trebuchet MS", Helvetica, sans-serif;
  margin: 0;
}

a {
  color: crimson;
  text-decoration: none;
}

a:hover {
  color: red;
}


/* Layout
------------------------------------------*/

header,
.container,
footer {
  margin: 0 auto;
  width: 88%;
  max-width: 1080px;
}

.wrapper {
  padding: 1em 0;
  background: rgba(255,255,255,0.5);
}


/* Animated background
------------------------------------------*/

@keyframes rainbow {
  0% {
    background-position:0% 50%;
  }
  25% {
    background-position:25% 50%;
  }
  50% {
    background-position:50% 50%;
  }
  75% {
    background-position:25% 50%;
  }
  100% {
    background-position:0% 50%;
  }
}

body {
  background: linear-gradient(30deg,orange,yellow,green);
  background-size: 800% 800%;
  animation: rainbow 10s infinite;
}