<div class="box"></div>
<div class="box"></div>
.box {
  display: inline-block;
  width: 300px;
  aspect-ratio: 1;
  margin: 10px;
  border: 2px solid red;
  background: radial-gradient(#000 60%,#0000 0)
}
.box + .box {
  background: radial-gradient(#000 60%,#0000 60.5%)
}
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