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How can I create Octagonal mask in CSS

I am trying to create a design in which images are octagonal in shape. I used the border hack, but the image needs to be inside the octagon shape. Using pesudo-elements is not apt in this case as the body will also have its own background image. Is it possible with css?

enter image description here

My Code

div {
	width: 100vh;
	height: 100vh;
	background: gold;
	position: relative;
}

div:before {
	content: "";
	position: absolute;
	top: 0;
	left: 0;
	border-bottom: 29vh solid gold;
	border-left: 29vh solid white;
	border-right: 29vh solid white;
	width: 42vh;
	height: 0;
}

div:after {
	content: "";
	position: absolute;
	bottom: 0;
	left: 0;
	border-top: 29vh solid gold;
	border-left: 29vh solid white;
	border-right: 29vh solid white;
	width: 42vh;
	height: 0;
}
<div></div>

I wanted this image to be in the golden area : http://images.visitcanberra.com.au/images/canberra_hero_image.jpg . Also, i used vh so that it is responsive to window height.

Solution

  • Fiddle

    With background image in fiddle: Fiddle

    <div class='octa'></div>

    CSS:

    Use image as background like this: background-image: url('http://lorempixel.com/400/400/nature');

    .octa {
  height: 250px;
  overflow: hidden;
  position: absolute;
  -webkit-transform: rotate(45deg);
  -moz-transform: rotate(45deg);
  transform: rotate(45deg);
  width: 250px;
}
.octa:after {
  background-color:#cecece;;
  bottom: 0;
  content: '';
  left: 0;
  position: absolute;
  right: 0;
  top: 0;
  -webkit-transform: rotate(45deg);
  -moz-transform: rotate(45deg);
  transform: rotate(45deg);
}

    enter image description here

    .octa {
  height: 100vh;
  overflow: hidden;
  position: absolute;
  transform: rotate(45deg);
  -webkit-transform: rotate(45deg);
  width: 100vh;
}
.octa:after {
  background-image: url(http://images.visitcanberra.com.au/images/canberra_hero_image.jpg);
  background-position: center center;
  background-size: auto 100vh;
  bottom: 0;
  content: '';
  left: 0;
  position: absolute;
  right: 0;
  top: 0;
  transform: rotate(-45deg);
  -webkit-transform: rotate(-45deg);
}
    <div class='octa'></div>