create a rainbow background using css linear gradient

HTML

<p>here is a more advanced example using 4 color points<p>
<div class='test-box linear-gradient-multi-rainbow'>multi point linear gradient</div>

CSS

.test-box {
  min-height:300px;
  width:100%;
  margin-bottom:20px;
  padding:20px;
  text-align:center;
  color:#FFF;
  text-shadow:0px 1px 2px #000;
}
.linear-gradient-multi-rainbow {
background:linear-gradient(45deg, #dc3b3e, #3b99dc 50%, #3bdc90 75%, rgb(255 141 0) 100%);
}