a标签中嵌套img和span，img和span中间留有巨大空白，这是为什么？

 a {
        float: left;
        width: 150rem/@baseFont;
        height: 140rem/@baseFont;
        text-align: center;

        img {
            display: block;
            width: 82rem/@baseFont;
            height: 82rem/@baseFont;
            margin: 10rem/@baseFont auto 0;
        }

        span {
            font-size: 25rem/@baseFont;
            color: #333;
        }
    }