flex水平居中并且高度自适应

水平居中并且高度自适应：

.btnBox {
    position: absolute;
    bottom: 0;
    left: 0;
    height: 10%;
    box-sizing: border-box;
    width: 100%;
    border-top: 1px solid #333;
    display: flex;
    justify-content: center;
    align-items: flex-start;
}

.btnBox a {
    border: 1px solid #333;
    padding: 8px 16px;
    margin: 15px;
    border-radius: 5px;
    display: inline-block;
}