How to Create a Transparent Half-Circle Cutout in a Div using Only CSS3?

Creating a Transparent Half-Circle Cutout in a Div using CSS3

To construct a transparent half-circle cutout within a div using only CSS3, the background color of all elements that form the shape must remain either black or transparent. A technique that meets this requirement involves utilizing CSS's ::after pseudo property.

Here is an example of how to achieve the desired effect:

body {
  background: green;
}

.rect {
  height: 100px;
  width: 100px;
  background: rgba(0, 0, 0, 0.5);
  position: relative;
  margin-top: 100px;
  margin-left: 100px;
}

.circle {
  display: block;
  width: 100px;
  height: 50px;
  top: -50px;
  left: 0;
  overflow: hidden;
  position: absolute;
}

.circle::after {
  content: '';
  width: 100px;
  height: 100px;
  -moz-border-radius: 100px;
  -webkit-border-radius: 100px;
  border-radius: 100px;
  background: rgba(0, 0, 0, 0);
  position: absolute;
  top: -100px;
  left: -40px;
  border: 40px solid rgba(0, 0, 0, 0.5);
}

<div class="rect"><span class="circle"></span></div>

This approach creates a rectangle with a black overlay and a semitransparent circle. The circle is positioned absolutely to create a transparent cutout shape.

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