擬似要素 before、after

before

.box-01

.box-01 {
  width: 300px;
  height: 300px;
  background-color: #cccccc;
  &::before {
    width: 60px;
    height: 60px;
    display: inline-block;
    content: "";
    background-color: red;
    border-radius: 50%;
  }
}

after

.box-02

.box-02 {
  width: 300px;
  height: 300px;
  background-color: #cccccc;
  &::before {
    width: 60px;
    height: 60px;
    display: inline-block;
    content: "";
    background-color: red;
    border-radius: 50%;
  }
}