<a class="btn-select" id="btn_select">
<select>
<option>选项一</option>
<option>选项二</option>
<option>选项三</option>
<option>选项四</option>
<option>选项五</option>
</select>
</a>

<form>
<a class="btn-select" id="btn_select">
<span class="cur-select">请选择</span>
<select>
<option>选项一</option>
<option>选项二</option>
<option>选项三</option>
<option>选项四</option>
<option>选项五</option>
</select>
</a>
</form>

* {
margin: 0;
padding: 0;
}
body {
padding: 50px 50px;
}
.btn-select {
position: relative;
display: inline-block;
width: 150px;
height: 25px;
background-color: #f80;
font: 14px/20px "Microsoft YaHei";
color: #fff;
}
.btn-select .cur-select {
position: absolute;
display: block;
width: 150px;
height: 25px;
line-height: 25px;
background: #f80 url(ico-arrow.png) no-repeat 125px center;
text-indent: 10px;
}
.btn-select:hover .cur-select {
background-color: #f90;
}
.btn-select select {
position: absolute;
top: 0;
left: 0;
width: 150px;
height: 25px;
opacity: 0;
filter: alpha(opacity: 0;);
font: 14px/20px "Microsoft YaHei";
color: #f80;
}
.btn-select select option {
text-indent: 10px;
}
.btn-select select option:hover {
background-color: #f80;
color: #fff;
}

var $$ = function (id) {
return document.getElementById(id);
}
window.onload = function () {
var btnSelect = $$("btn_select");
var curSelect = btnSelect.getElementsByTagName("span")[0];
var oSelect = btnSelect.getElementsByTagName("select")[0];
var aOption = btnSelect.getElementsByTagName("option");
oSelect.onchange = function () {
var text=oSelect.options[oSelect.selectedIndex].text;
curSelect.innerHTML = text;
}
}