<input type="radio" name="e">

<input type="radio" name="e" class="round">

input {
  width: 40px;
  height: 40px;
  border: 5px solid grey;
  padding: 5px;
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  cursor:pointer;
}
input:checked {
  background: green content-box;
  border-color: green;
}

.round {
  border-radius:50%;
}

body {
  background: pink;
  display: grid;
  height: 100vh;
  margin:0;
  grid-auto-flow :column;
  place-content: center;
  gap: 40px;
}