<div class="container">
  <div class="wrapper">
    <input type="checkbox" name="mode" id="switcher">
    <label for="switcher">Toggle filter</label>
    <img src="http://web.archive.org/web/20170502125106im_/https://storage.googleapis.com/imgfave/image_cache/1315195549154431.jpg">
    <div class="warning">
      <p>Warning: Graphic content. Click the red button to reveal.</p>
    </div>
  </div>
</div>

body {
  background-color: #F5F5F5;
  color: #fff;
  font-size: 1.1em;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

.container {
  margin: 1em auto;
  max-width: 700px;
}

.wrapper {
  height: 395px;
  width: 500px;
  position: relative;
}

input {
  display: none;
}

label {
  position: absolute;
  z-index: 1;
  background-color: red;
  padding: 1em;
  cursor: pointer;
  transition: background-color 0.3s ease;
}

label:hover {
  background-color: firebrick;
}

img {
  width: 100%;
  height: 100%;
  position: absolute;
  left: 0;
}

.warning {
  position: absolute;
  text-align: center;
  height: 100%;
  width: 100%;
  background-color: rgba(0, 0, 0, 0.75);
  -webkit-backdrop-filter: contrast(4) blur(20px);
  backdrop-filter: contrast(4) blur(20px);
  display: flex;
  align-items: center;
  justify-content: center;
}

input:checked ~ .warning {
  background-color: rgba(0, 0, 0, 0);
  -webkit-backdrop-filter: blur(0);
  backdrop-filter: blur(0);
}

input:checked ~ .warning p {
  color: transparent;
}