Create a Reverse Clip-Path - CSS or SVG

Question

I'm trying to create what is in essence the reverse of a CSS clip-path. When using clip-path, an image or div is clipped so that only the shape you specify remains and the rest of the background is effectively deleted.

I would like it so that if I clip a shape it basically punches a hole in the upper most layer and removes the shape, not the background. Is this possible? I'd also be open to an SVG solution, but I am new to SVG so be kind :)

Basically, in the code below I have a blue square positioned absolutely inside a red square and want to be able to punch a shape out of the blue square so the red layer below shows through where the shape used to be. In reality there will an image as the background layer, so I can't accept a pseudo effect that mimics what I want but doesn't actually punch the shape out.

Any assistance would be amazing!

codepen: https://codepen.io/emilychews/pen/GQmyqx

body {
  width: 100%; 
  height: 100vh;
  padding: 0; margin: 0;
  display: flex;
  }

#box {
  margin: auto;
  position: relative;
  width: 33%;
  height: 200px;
  background: red;
}

#innerbox {
  width: 100%;
  height: 100%;
  background: blue;
  top: 0;
  left: 0;
  position: absolute;
}

<div id="box">
  <div id="innerbox"></div>
</div>

Answer 1

This ranks high on Google and the answer didn't solve my problem b/c I cannot touch my background image so here is another way of doing this:

Create a frame with the clip path.

body {
  width: 100%;
  height: 100vh;
  padding: 0;
  margin: 0;
  display: grid;
  place-items: center;
}

#clip,
#background {
  width: 400px;
  height: 400px;
}

#clip {
  clip-path: polygon(0% 0%, 0% 100%, 25% 100%, 25% 25%, 75% 25%, 75% 75%, 25% 75%, 25% 100%, 100% 100%, 100% 0%);
  position: absolute;
  background: #fff;
  opacity: 0.8;
}

#background {
  background: url(https://lorempixel.com/400/400/) center/cover;
  z-index: -1;
}

<div id="background">
  <div id="clip"></div>
</div>

I put the clip-div inside the image because of convenience but you can also have it outside. However make sure that you are okay with the limited browser support of clip-path.

Answer 2

You can put the image above the blue part and you apply the clip-path on it then the result will be the same as if you have created a hole inside the blue part to see the image below:

body {
  width: 100%; 
  height: 100vh;
  padding: 0; margin: 0;
  display: flex;
  }

#box {
  margin: auto;
  position: relative;
  width: 33%;
  height: 200px;
  background: blue;
}

#innerbox {
  width: 100%;
  height: 100%;
  background: url(https://lorempixel.com/400/400/) center/cover;
  top: 0;
  left: 0;
  position: absolute;
  z-index:1;
  clip-path:polygon(10% 10%, 10% 90%, 90% 50%);
}

<div id="box">
  <div id="innerbox"></div>
</div>

Another idea is to consider multiple background and you will have better support than clip-path and also less of code:

body {
  height: 100vh;
  margin: 0;
  display: flex;
}

#box {
  margin: auto;
  position: relative;
  width: 33%;
  height: 200px;
  background: 
    linear-gradient(to bottom right,transparent 49%,blue 50%) bottom/100% 60%,
    linear-gradient(to top right,transparent 49%,blue 50%) top/100% 60%,
    linear-gradient(blue,blue) left/20% 100%,
    url(https://lorempixel.com/400/400/) center/cover;
  background-repeat:no-repeat;
}

<div id="box">
</div>

UPDATE

If you want some opacity, here is an idea where you have to duplicate the content using clip-path (a drawback):

body {
  width: 100%; 
  height: 100vh;
  padding: 0; margin: 0;
  display: flex;
  }

#box {
  margin: auto;
  position: relative;
  width: 33%;
  height: 200px;
  background: blue;
}

#innerbox,#innerbox-2 {
  width: 100%;
  height: 100%;
  background: url(https://lorempixel.com/400/400/) center/cover;
  top: 0;
  left: 0;
  position: absolute;
  z-index:2;
}
#innerbox {
  /* if you initially planned to have x opacity so you need to set 1-x here*/
  opacity:0.4;
}

#innerbox-2 {
  z-index:1;
  clip-path:polygon(10% 10%, 10% 90%, 90% 50%);
  animation:animate 5s linear alternate infinite;
}

@keyframes animate {
  from {
    clip-path:polygon(10% 10%, 10% 90%, 90% 50%);
  }
  to {
     clip-path:polygon(20% 50%, 90% 50%, 80% 10%);
  }
}

<div id="box">
  <div id="innerbox">
    <h1>Title</h1>
    <p>Some content</p>
  </div>
  <div id="innerbox-2">
    <h1>Title</h1>
    <p>Some content</p>
  </div>
</div>