How to create a slanted rectangle using ::after code example

Example 1: css circle

#circle {
      width: 100px;
      height: 100px;
      background: red;
      border-radius: 50%
    }

Example 2: how to create a circle with css

<div id="circle">
</div>

#circle {
    width: 100px;
    height: 100px;
    background: red;
    border-radius: 50%
}