標籤高度爲百分百後。利用flex垂直居中

<div class="top_title">
     <span>xxxxxxxx系統</span>
</div>



    .top_title span {
        width: 60%;
        height: 100%;
        background: url('./img/top.png')no-repeat;
        background-size: 100% 100%;
        display: flex;
        align-items: center;
        justify-content: center;
        text-align: justify;
        margin: 0 auto;
        font-size: 2.5rem;
        color: #58aada;
        font-weight: bold;
    }

當然還有其他方法。下期再講。