CSS design - rainbow

Question

I want to create a rainbow using only CSS only. Below is an image of what is required.

Here is my code (so far):

* {
  margin: 0;
  padding: 0;
}
#r {
  height: 80vw;
  width: 80vw;
  background-color: #f00;
  position: absolute;
  z-index: 1;
}
#o {
  height: 76vw;
  width: 76vw;
  background-color: #fe6230;
  position: absolute;
  top: 2vw;
  left: 2vw;
  z-index: 2;
}
#y {
  height: 72vw;
  width: 72vw;
  background-color: #fef600;
  position: absolute;
  top: 4vw;
  left: 4vw;
  z-index: 3;
}
#g {
  height: 68vw;
  width: 68vw;
  background-color: #00bc00;
  position: absolute;
  top: 6vw;
  left: 6vw;
  z-index: 4;
}
#b {
  height: 64vw;
  width: 64vw;
  background-color: #0048fe;
  position: absolute;
  top: 8vw;
  left: 8vw;
  z-index: 5;
}
#i {
  height: 60vw;
  width: 60vw;
  background-color: #000083;
  position: absolute;
  top: 10vw;
  left: 10vw;
  z-index: 6;
}
#v {
  height: 56vw;
  width: 56vw;
  background-color: #30009b;
  position: absolute;
  top: 12vw;
  left: 12vw;
  z-index: 7;
}

<div id="r">
</div>
<div id="o">
</div>
<div id="y">
</div>
<div id="g">
</div>
<div id="b">
</div>
<div id="i">
</div>
<div id="v">
</div>

The problem with my code is that I am unable to curve it (like in a real rainbow). I also need to hide half of this rainbow.

Answer 1

This could be done using a single div element with a :pseudo-element and box-shadow.

div {
  position: relative;
  width: 300px;
  height: 150px;
  background: white;
  overflow: hidden;
  transform: scale(2);
  margin-left: 130px;
  margin-top: -50px;
}
div:after {
  position: absolute;
  content: '';
  width: 100px;
  height: 100px;
  top: 100px;
  left: 50px;
  border-radius: 50%;
  box-shadow: 0 0 0 5px #4200AB, 0 0 0 10px #000095, 0 0 0 15px #00ABFF, 0 0 0 20px #00C800, 0 0 0 25px #FFF800, 0 0 0 30px #FF7642, 0 0 0 35px #E40000;
}

<div></div>

Example using vh / vw units.

Demo on CodePen

Looks awful in the snippet here because of the viewport ratio, better viewed on CodePen.

div {
  position: relative;
  width: 95vw;
  height: 45vw;
  overflow: hidden;
  background: transparent;
  transform: translate(-50vw, -16.666vw);
  top: 8vw;
  left: 50vw;
}
div:after {
  position: absolute;
  content: '';
  width: 50%;
  height: 100%;
  top: 25vw;
  left: 25vw;
  border-radius: 50%;
  box-shadow: 0 0 0 2vw #4200AB, 0 0 0 4vw #000095, 0 0 0 6vw #00ABFF, 0 0 0 8vw #00C800, 0 0 0 10vw #FFF800, 0 0 0 12vw #FF7642, 0 0 0 14vw #E40000;
}
body {
  margin: 0;
}

<div></div>