select框高度问题

<div class="article-start-box"> <span class="categery">分类栏目</span> <select style="position: absolute;z-index: 1;margin-left: 40px;" class="choose" onmousedown="if(this.options.length>6){this.size=7}" onblur="this.size=0" onchange="this.size=0"> <option value="volvo">文学集</option> <option value="saab">哲学</option> <option value="opel">雅思</option> <option value="audi">大学网奥数大学网奥数</option> <option value="volvo">文学集</option> <option value="saab">哲学</option> <option value="opel">雅思</option> <option value="audi">大学网奥数</option> </select> </div>