修改下拉框的样式

css

.select-bg {
    display: inline-block;
    width: 85px;
    height: 20px;
    line-height: 20px;
    font-size: 12px;
    border: #089164 solid 1px;
    background: #fff url(../img/select.png) no-repeat right center;
    background-size: 30px 20px;
    vertical-align: middle;
    cursor: pointer;
}
.select-green {
    -webkit-appearance: none;
       -moz-appearance: none;
            appearance: none;
    position: relative;
    top: -3px;
    outline: none;
    border: 0 none;
    position: relative;
    padding: 0 0 0 5px;
    width: 85px;
    background: none;
    background-color: transparent;
    font-size: 12px;
    z-index: 99;
    overflow: hidden;
}

html

<div class="select-bg">                     
    <select class="select-green" id="selectTime">
        <option value="60">1小时</option>
        <option value="360" selected>6小时</option>
        <option value="1440">1天</option>
        <option value="4320">3天</option>
        <option value="11520">8天</option>
        <option value="21600">15天</option>
    </select>