/*
 * 简洁的垂直居中样式
 * <div class="vcenter"><div>内容(此div需要设置一个高度属性)</div></div>
 * 更多居中方式参考: http://blog.csdn.net/freshlover/article/details/11579669
 */
.abs-vcenter {
    position: relative;
}

.abs-vcenter > div {
    margin: auto;
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    overflow: auto;
}

/*
 * 借用 button 特性实现垂直居中显示
 * <button class="content-middle"><span>内容</span></button>
 */
button.btn-vcenter {
    background: none;
    border: none;
    outline: none;
    cursor: default;
}

button.btn-vcenter > span {
    position: relative;
    top: 0;
    left: 0;
}