去到底部、回到顶部css当网页向下滑动 20px 出现"返回顶部" 按钮

html

<div>
        <button onclick="returnTop()" id="btnTop" title="返回顶部">返回顶部</button>
        <button onclick="returnBottom()" id="btnBottom" title="去到底部">去到底部</button>
    </div>

样式

#btnTop {
        display: none;
        position: fixed;
        bottom: 20px;
        right: 30px;
        z-index: 99;
        border: none;
        outline: none;
        background-color: #89cff0;
        color: white;
        cursor: pointer;
        padding: 15px;
        border-radius: 10px;
    }

    #btnTop:hover {
        background-color: #1E90FF;
    }

    #btnBottom {
        display: none;
        position: fixed;
        bottom: 100px;
        right: 30px;
        z-index: 99;
        border: none;
        outline: none;
        background-color: #89cff0;
        color: white;
        cursor: pointer;
        padding: 15px;
        border-radius: 10px;
    }

    #btnBottom:hover {
        background-color: #1E90FF;
    }

js

// 当网页向下滑动 20px 出现"返回顶部" 按钮
    window.onscroll = function () {
        scrollFunction();
    };

    function scrollFunction() {
        if (document.body.scrollTop > 20 || document.documentElement.scrollTop > 20) {
            $("#btnTop").css("display", "block");
            $("#btnBottom").css("display", "block");
        } else {
            $("#btnTop").css("display", "none");
            $("#btnBottom").css("display", "none");
        }
    }

    // 点击按钮，返回顶部
    function returnTop() {
        document.body.scrollTop = 0;
        document.documentElement.scrollTop = 0;
    }

    function returnBottom() {
        document.body.scrollTop = document.body.clientHeight;
        document.documentElement.scrollTop = document.body.clientHeight;
    }

来源：https://blog.csdn.net/weixin_42171955/article/details/100983968