W3School TIY Editor

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
/* 容器必须相对定位： */
.custom-select {
  position: relative;
  font-family: Arial;
}

.custom-select select {
  display: none; /* 隐藏原始 SELECT 元素： */
}

.select-selected {
  background-color: DodgerBlue;
}

/* 设置选择元素内箭头的样式： */
.select-selected:after {
  position: absolute;
  content: "";
  top: 14px;
  right: 10px;
  width: 0;
  height: 0;
  border: 6px solid transparent;
  border-color: #fff transparent transparent transparent;
}

/* 当选择框打开（活动）时，将箭头指向上方： */
.select-selected.select-arrow-active:after {
  border-color: transparent transparent #fff transparent;
  top: 7px;
}

/* 设置项目（选项）的样式，包括所选项目： */
.select-items div,.select-selected {
  color: #ffffff;
  padding: 8px 16px;
  border: 1px solid transparent;
  border-color: transparent transparent rgba(0, 0, 0, 0.1) transparent;
  cursor: pointer;
}

/* 设置项目（选项）的样式： */
.select-items {
  position: absolute;
  background-color: DodgerBlue;
  top: 100%;
  left: 0;
  right: 0;
  z-index: 99;
}

/* 关闭选择框时隐藏项目： */
.select-hide {
  display: none;
}

.select-items div:hover, .same-as-selected {
  background-color: rgba(0, 0, 0, 0.1);
}
</style>
</head>

<body>

<h2>自定义选择菜单</h2>

<div class="custom-select" style="width:200px;">
  <select>
    <option value="0">Select car:</option>
    <option value="1">Audi</option>
    <option value="2">BMW</option>
    <option value="3">Citroen</option>
    <option value="4">Ford</option>
    <option value="5">Honda</option>
    <option value="6">Jaguar</option>
    <option value="7">Land Rover</option>
    <option value="8">Mercedes</option>
    <option value="9">Mini</option>
    <option value="10">Nissan</option>
    <option value="11">Toyota</option>
    <option value="12">Volvo</option>
  </select>
</div>

/* 如果用户单击选择框之外的任意位置，则关闭所有选择框： */
document.addEventListener("click", closeAllSelect);
</script>

</body>
</html>