如何自訂 HTML `` 元素中所選選項的背景顏色？

<div class="custom-select">
  <select>

.custom-select {
  position: relative;
  width: 200px;
}

.custom-select select {
  display: none;
}

.custom-select-overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: red;
  opacity: 0;
  transition: opacity 0.2s ease-in-out;
}

.custom-select:hover .custom-select-overlay {
  opacity: 0.5;
}

.custom-select select:focus + .custom-select-overlay {
  opacity: 1;
}