SOURCE

<div class="toolbar">
    <ul>
        <li><a href="#"><img src="https://hjd6633.oss-cn-hangzhou.aliyuncs.com/notes/html_css/0203_jd/index.png"></a></li>
        <li><a href="#"><img src="https://hjd6633.oss-cn-hangzhou.aliyuncs.com/notes/html_css/0203_jd/classify.png"></a></li>
        <li><a href="#"><img src="https://hjd6633.oss-cn-hangzhou.aliyuncs.com/notes/html_css/0203_jd/car.png"></a></li>
        <li><a href="#"><img src="https://hjd6633.oss-cn-hangzhou.aliyuncs.com/notes/html_css/0203_jd/login.png"></a></li>
    </ul>
</div>

body{
    height: 1000px;
    width: 375px;
    width: 420px;
}

*{
    margin:0;
    padding:0;
}
li{
    list-style: none;
}

.toolbar{
    background-color: #ccc;
    
    position: fixed;
    bottom: 100px;
    left: 0;
}

.toolbar ul{
    display: flex;
}

.toolbar ul li{
    width: 25%;
    height: 50px;

    /* 让图片居中对齐, 图片也是行内元素 */
    text-align: center;
}

.toolbar ul li img{
    height: 50px;
    vertical-align: middle;
}