css定位

                <div class="dropdown-menu" id="dropdown-menu">
                    <a class="button-green" style="margin-top:18px;">查找好友</a>
                    <a class="button-green">查找群组</a>
                    <a class="button-green">创建群组</a>
                    <a id="logout" class="button-red">退出帐号</a>
                </div>

* {
  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box;
          position: relative;
          z-index: inherit;
}
*:before,
*:after {
  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box;
          position: relative;
          z-index: inherit;
}
.dropdown-menu {
    display: block;
    background:#e6e6e6;
    box-shadow:0 0 16px 0 rgba(0,0,0,0.18), 0 16px 16px 0 rgba(0,0,0,0.24);
    border-radius:8px;
    width:160px;
    height:198px;
    position: absolute;
    padding-left:16px;
    z-index: 9999;
    margin-top:0;
    left: auto;
    right: 0;
    top: 0;
    float:right;
}
.button-green {
    background:#19bb9b;
    /*background-image: url(‘/image/button-green.png‘);*/
}
.button-red {
    background:#d43044;
    /*background-image: url(‘/image/button-red.png‘);*/
}
.button-green,
.button-red {
    display: block;
    position: relative;
    z-index: inherit;
    border-radius:9px;
    background-position: center;
    width:83.125%;
    height:35px;
    margin-top: 8px;
    /*padding: 7px 37px 11px 38px;*/
    padding: 7px;
    background-repeat: repeat-x;
    /*font*/
    font-size:14px;
    color:#ffffff;
    text-align: center;
}