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  • 移动端常用单位——rem

    移动端常用单位：
①px：像素大小，固定值
②%：百分比
③em（不常用，但是在首行缩进时可以使用）：相对自身的font大小（当自身的字体大小也是em做单位时，才会以父元素的字体大小为基准单位）
④rem（移动端主流）：相对根节点(html)的font大小
⑤vw（视口宽度）：相对视口宽度比例，1vw相当于视口宽度的百分之一
⑥vh（视口高度）：相对视口高度比例，1vh相当于视口高度的百分之一


视口宽度（clientWidth）用JS获取,修改html{ font-size : ?rem } 从而动态调整flex布局宽高：docEl.style.fontsize = viewWidth/375*20+'px';
移动端rem目前还是主流

    <!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
    <title>3.9 移动端常用单位</title>
    <link rel="stylesheet" href="css/iconfont.css">
    <style>
        /*px/%/em/rem/vw/vh*/

        /*css reset*/
            * {
                box-sizing: border-box;
                padding: 0;
                margin: 0;
            }
            body {
                background-color: #e2e2e2;
                color: #595B66;
            }
            a {
                font-size: 12px;
                color: #686868;
                text-decoration: none;
            }
            li {
                list-style: none;
            }

        /*body {
            font-size: 20px;
        }*/

        html {
            font-size: 12px;
        }
        .tabbar-container {
            position: fixed;
            left: 0;
            bottom: 0;
            z-index: 1000;
            width: 100%;
            
            /*height: 5em;
            font-size: 12px;*/
            /*font-size: 12em;*/

            /*height: 5rem;*/

            /* 100vw;
            height: 10vh;*/
            background-color: #fff;
            box-shadow: 0 0 10px 0 rgba(154, 141 ,141, 0.6);

            height: 50px;
            /*
                height
                    375px -> 100%(375px) x 50px
                    750px -> 100%(750px) x 100px
                    ?(视口宽度) -> (? / 750) * 100 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    height = (document.documentElement.clientWidth / 750) * 100 px
                    height = (document.documentElement.clientWidth / 375) * 50 px
            */

            /*
                用px/em做单位，每次都要用js一一修改
                能不能统一修改呢？
                    375px -> 1rem = 20px;
                        height = 50 / 20 = 2.5rem;
                    750px -> 1rem = 40px;
                        height = 100 / 40 = 2.5rem;
                    ?(视口宽度) -> 1rem = (? / 375) * 20 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    1rem = (document.documentElement.clientWidth / 375) * 20 px
                    1rem = (document.documentElement.clientWidth / 750) * 40 px
                    height = 2.5rem;
            */
            /*375px 1rem = 20px;*/
            height: 2.5rem;
        }
        .tabbar-link .iconfont {
            /*font-size: 24px;*/
            font-size: 1.2rem;
            /*font-size: 2em;*/

            /*
                font-size
                    375px -> 24px
                    750px -> 48px
                    ?(视口宽度) -> (? / 750) * 48 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    font-size = (document.documentElement.clientWidth / 750) * 48 px
                    font-size = (document.documentElement.clientWidth / 375) * 24 px
            */
            /*
                用px/em做单位，每次都要用js一一修改
                能不能统一修改呢？
                    375px -> 1rem = 20px;
                        font-size = 24 / 20 = 1.2rem;
                    750px -> 1rem = 40px;
                        font-size = 48 / 40 = 1.2rem;
                    ?(视口宽度) -> 1rem = (? / 375) * 20 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    1rem = (document.documentElement.clientWidth / 375) * 20 px
                    1rem = (document.documentElement.clientWidth / 750) * 40 px
                    font-size = 1.2rem;
            */
        }
        .tabbar,
        .tabbar-item,
        .tabbar-link {
            height: 100%;
        }
        .tabbar {
            display: flex;
        }
        .tabbar-item {
            flex: 1;
        }
        .tabbar-link {
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;

            font-size: 0.6rem;
        }
        .tabbar-item-active .tabbar-link {
            color: #de181b;
        }
    </style>
</head>
<body>

    <!-- <p style="text-indent: 2em;">
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
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        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
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        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
    </p> -->

    <div class="tabbar-container">
        <ul class="tabbar">
            <li class="tabbar-item tabbar-item-active">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-home"></i>
                    <span>首页</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-category"></i>
                    <span>分类页</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-cart"></i>
                    <span>购物车</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-personal"></i>
                    <span>个人中心</span>
                </a>
            </li>
        </ul>
    </div>

    <script>
        setRemUnit();

        window.onresize = setRemUnit;

        function setRemUnit() {
            var docEl = document.documentElement;
            var viewWidth = docEl.clientWidth;

            docEl.style.fontSize = viewWidth / 375 * 20 + 'px';
            // docEl.style.fontSize = viewWidth / 750 * 40 + 'px';
            // 1rem = 20px
        }
    </script>
</body>
</html>
    <!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
    <title>3.9 移动端常用单位</title>
    <link rel="stylesheet" href="css/iconfont.css">
    <style>
        /*px/%/em/rem/vw/vh*/

        /*css reset*/
            * {
                box-sizing: border-box;
                padding: 0;
                margin: 0;
            }
            body {
                background-color: #e2e2e2;
                color: #595B66;
            }
            a {
                font-size: 12px;
                color: #686868;
                text-decoration: none;
            }
            li {
                list-style: none;
            }

        /*body {
            font-size: 20px;
        }*/

        html {
            font-size: 12px;
        }
        .tabbar-container {
            position: fixed;
            left: 0;
            bottom: 0;
            z-index: 1000;
            width: 100%;
            
            /*height: 5em;
            font-size: 12px;*/
            /*font-size: 12em;*/

            /*height: 5rem;*/

            /* 100vw;
            height: 10vh;*/
            background-color: #fff;
            box-shadow: 0 0 10px 0 rgba(154, 141 ,141, 0.6);

            height: 50px;
            /*
                height
                    375px -> 100%(375px) x 50px
                    750px -> 100%(750px) x 100px
                    ?(视口宽度) -> (? / 750) * 100 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    height = (document.documentElement.clientWidth / 750) * 100 px
                    height = (document.documentElement.clientWidth / 375) * 50 px
            */

            /*
                用px/em做单位，每次都要用js一一修改
                能不能统一修改呢？
                    375px -> 1rem = 20px;
                        height = 50 / 20 = 2.5rem;
                    750px -> 1rem = 40px;
                        height = 100 / 40 = 2.5rem;
                    ?(视口宽度) -> 1rem = (? / 375) * 20 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    1rem = (document.documentElement.clientWidth / 375) * 20 px
                    1rem = (document.documentElement.clientWidth / 750) * 40 px
                    height = 2.5rem;
            */
            /*375px 1rem = 20px;*/
            height: 2.5rem;
        }
        .tabbar-link .iconfont {
            /*font-size: 24px;*/
            font-size: 1.2rem;
            /*font-size: 2em;*/

            /*
                font-size
                    375px -> 24px
                    750px -> 48px
                    ?(视口宽度) -> (? / 750) * 48 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    font-size = (document.documentElement.clientWidth / 750) * 48 px
                    font-size = (document.documentElement.clientWidth / 375) * 24 px
            */
            /*
                用px/em做单位，每次都要用js一一修改
                能不能统一修改呢？
                    375px -> 1rem = 20px;
                        font-size = 24 / 20 = 1.2rem;
                    750px -> 1rem = 40px;
                        font-size = 48 / 40 = 1.2rem;
                    ?(视口宽度) -> 1rem = (? / 375) * 20 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    1rem = (document.documentElement.clientWidth / 375) * 20 px
                    1rem = (document.documentElement.clientWidth / 750) * 40 px
                    font-size = 1.2rem;
            */
        }
        .tabbar,
        .tabbar-item,
        .tabbar-link {
            height: 100%;
        }
        .tabbar {
            display: flex;
        }
        .tabbar-item {
            flex: 1;
        }
        .tabbar-link {
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;

            font-size: 0.6rem;
        }
        .tabbar-item-active .tabbar-link {
            color: #de181b;
        }
    </style>
</head>
<body>

    <!-- <p style="text-indent: 2em;">
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        我是短路
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
        adasdasdasdasd
    </p> -->

    <div class="tabbar-container">
        <ul class="tabbar">
            <li class="tabbar-item tabbar-item-active">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-home"></i>
                    <span>首页</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-category"></i>
                    <span>分类页</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-cart"></i>
                    <span>购物车</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-personal"></i>
                    <span>个人中心</span>
                </a>
            </li>
        </ul>
    </div>

    <script>
        setRemUnit();

        window.onresize = setRemUnit;

        function setRemUnit() {
            var docEl = document.documentElement;
            var viewWidth = docEl.clientWidth;

            docEl.style.fontSize = viewWidth / 375 * 20 + 'px';
            // docEl.style.fontSize = viewWidth / 750 * 40 + 'px';
            // 1rem = 20px
        }
    </script>
</body>
</html>
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  • 原文地址：https://www.cnblogs.com/rickdiculous/p/11530967.html
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