Three colors angled background color

Question

How could I achieve a background that looked similar to this image:

Only 3 colors, angled from the top corner out like a sunray.

Maybe sticking with a simple PNG or SVG background image would be a better approach.

Answer 1

The effect can be achieved with CSS using pseudo-elements and transforms and the below is a sample snippet. But I don't think using CSS is the correct option for this. It would be better to use a PNG image.

The snippet uses a couple of pseudo-elements with different background colors skewed at required angles to produce the three-color effect.

.bg {
  position: relative;
  height: 200px;
  width: 400px;
  padding: 4px;
  background: orange;
  overflow: hidden;
}
.bg:after,
.bg:before {
  position: absolute;
  content: '';
  left: 0px;
  height: 100%;
  width: 100%;
  transform-origin: right top;
}
.bg:before {
  top: 0px;
  background: red;
  transform: skewY(-45deg);
}
.bg:after {
  top: -100%;
  background: yellow;
  transform: skewY(-15deg);
}
span {
  position: relative;
  z-index: 2;
}

/* Just for demo */
.bg:hover {
  height: 200px;
  width: 500px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/prefixfree/1.0.7/prefixfree.min.js"></script>
<div class="bg">
  <span>Some content inside</span>
</div>

Angled linear-gradients also could be used but I don't think they are good for dynamic sized container elements as the angles need to be modified as the dimensions change to keep the appearance the same.

Below is a snippet using linear-gradient. Hover on the shape to see how a change of width and/or height affects it.

.bg {
  position: relative;
  height: 200px;
  width: 400px;
  background: linear-gradient(310deg, red 30%, transparent 30%), linear-gradient(340deg, transparent 58%, yellow 58%), orange;
  overflow: hidden;
}
.bg:hover {
  height: 200px;
  width: 500px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/prefixfree/1.0.7/prefixfree.min.js"></script>
<div class="bg">
  <span>Some content inside</span>
</div>

Answer 2

SVG

This can be done with SVG. I used three polygon shapes. This can be set to a background-image. Or alternatively can be used inline so you can use css properties on it.

html, body {
  margin: 0;
  padding: 0;
}
.triple {
  width: 250px;
  height: 250px;
}
.triple:hover {
  width: 500px;
  height: 100px;
}

<svg class="triple" viewBox="0 0 100 100" preserveAspectRatio="none">
  <polygon fill="#dd2" points="0,0 100,0 0,60" />
  <polygon fill="#bb2" points="0,60 100,0 30,100 0,100 " />
  <polygon fill="#992" points="30,100 100,0 100,100" />
</svg>