1. 在博客后台选择皮肤主题、申请js权限等

我选的主题是SimpleMemory

2. 在博客设置页添加页面css代码如下

body {
    background-image: url(https://images.cnblogs.com/cnblogs_com/blogs/786357/galleries/2285082/o_230309173325_bg_image.jpg);
    background-repeat: no-repeat;
    background-size: 100% 100vh;
    background-attachment: fixed;
}
#home {
    background-color: rgba(255, 255, 255, 0.3);
    margin: 0 auto;
    width: 90%;
    min-width: 950px;
    padding: 30px;
    margin-top: 50px;
    margin-bottom: 50px;
    box-shadow: 0 2px 6px rgba(100,100,100,.3);
}
.navbar {
    box-shadow: 0 2px 6px rgb(100 100 100 / 15%);
}
.navbar {
    display: flex;
    flex-direction: column;
    align-items: center;
    background-color: #fff;
    padding-left: 40px;
    padding-right: 40px;
    padding-top: 5px;
    padding-bottom: 5px;
    background-color: rgba(255, 255, 255, 0.7);
}
.navbar>nav {
    font-size: 15px;
    display: flex;
    color: rgb(58, 58, 58);
    flex-direction: row;
    flex-wrap: nowrap;
    align-items: center;
    justify-content: space-between;
    width: 100%;
}
.navbar>nav a:hover {
    color: rgb(0, 145, 189);
}
#home a {
    text-decoration: none;
}
#header a {
    text-decoration: none;
    color: #000;
}
#header a:hover {
    color: #666;
}
#header>#blogTitle {
    font-family: "华文彩云";
    font-size: 20px;
    line-height: 22px;
}
#navigator {
    display: flex;
    flex-direction: row;
}
#navigator>#navList {
    display: flex;
    flex-direction: row;
    list-style-type: none;
    font-family: "华文隶书";
    margin-right: 100px;
}
#navigator>#navList a {
    display: inline-block;
    margin-right: 20px;
    font-size: 22px;
}
#navigator>.blogStats {
    padding-top: 15px;
    font-size: 18px;
    font-family: "华文新魏";
}
#main {
    width: 100%;
    text-align: left;
    margin-top: 30px;
    display: flex;
    flex-direction: row;
}
#mainContent {
    flex: 1;
    min-height: 200px;
    -o-text-overflow: ellipsis;
    text-overflow: ellipsis;
    overflow: hidden;
    margin: 0 5px;
    background-color: rgba(255, 255, 255, 0.4);
}
#mainContent .forFlow {
    float: none;
    width: auto;
    padding: 15px;
}
#mainContent .forFlow .dayTitle {
    display: none;
}
#topics .postTitle {
    border: 0;
    font-weight: bold;
    line-height: 1.5;
    width: 100%;
    padding-left: 5px;
    text-decoration: none;
}
.postTitle a {
    font-size: 35px;
    color: rgb(0, 0, 186);
    font-family: "华文行楷";
}
.postTitle a:hover {
    color: #519bf0;
}
.postTitle a:link, .postTitle a:visited, .postTitle a:active {
    transition: all .4s linear 0s;
}

#sideBar {
    width: 260px;
    min-height: 200px;
    padding: 0 0 0 5px;
    float: right;
    -o-text-overflow: ellipsis;
    text-overflow: ellipsis;
    overflow: hidden;
    font-size: 12px;
    margin: -15px 5px 0 5px;
}
#blog-calendar {
    width: 228px;
    padding-bottom: 5px;
    margin-bottom: 40px;
    margin-top: 40px;
    box-shadow: 0 1px 3px #ccc;
    border: 1px solid #ededed;
    background: rgba(247, 247, 247, 0.6);
}
#blog-calendar th {
    font-size: 12px;
}
#blogCalendar {
    border-collapse: collapse;
    border-spacing: 0;
    border: none;
    color: #666;
}
#blogCalendar td {
    padding-top: 4px;
    padding-bottom: 4px;
}
#blogCalendar tbody {
    display: table-row-group;
    vertical-align: middle;
    border-color: inherit;
}
.CalTitle {
    width: 100%;
    text-align: center;
    font-size: 14px;
    font-weight: bold;
    padding: 5px 0;
}
.CalTitle td {
    background: rgba(247, 247, 247, 0.7); !important;
    border: 0 !important;
    color: #5e5f63;
    font-family: "Comic Sans MS";
}
.CalNextPrev {
    color: #000;
}
.CalDayHeader {
    background: rgba(247, 247, 247, 0.7);
    font-weight: bold;
    color: #5e5f63;
}
.CalOtherMonthDay {
    color: #bbb;
}
.CalTodayDay {
    background: #3671a5 !important;
    color: #fff;
    font-weight: bold;
}
.sidebar-block a,
.sidebar-block span,
.sidebar-block p {
    color: #333;
    font-family: "华文中宋";
    font-size: 15px;
}
.sidebar-block a:hover {
    color: #0169e1;
}
.sidebar-block ul {
    list-style-type: none;
}
#sideBar .catListTitle {
    font-family: "华文隶书";
    font-size: 20px;
    font-weight: 200;
}
.div_my_zzk {
    width: 175px;
    position: relative;
    margin-top: 10px;
}
.input_my_zzk {
    border: 1px solid #ccc;
    height: 25px;
    padding-right: 30px;
    padding-left: 5px;
    width: 100%;
    outline: 0;
    vertical-align: middle;
    background-color: rgba(248, 248, 248, 0.6);
}
.btn_my_zzk {
    font-size: 12px;
    width: 25px;
    height: 25px;
    color: transparent;
    border: 0;
    border-style: none;
    cursor: pointer;
    top: 1px;
    position: absolute;
    right: -35px;
}
#btnZzk {
    background: url(https://www.cnblogs.com/skins/simplememory/images/blog_search.png) no-repeat 5px 5px;
}
#widget_my_google input[type=button] {
    background: url(https://www.cnblogs.com/skins/simplememory/images/google_search.png) no-repeat 5px 5px;
}
#profile_block,
#profile_block a {
    font-family: "华文中宋";
    font-size: 15px;
    color: #333;
}
#profile_block a:hover {
    color: #0169e1;
}
.RecentCommentBlock p {
    font-size: 12px;
    padding-left: 20px;
}
.recent_comment_title p {
    padding-left: 0;
}

#cnblogs_post_body {
    padding-bottom: 20px;
    border-bottom: #5F5A4B 4px solid;
}
#cnblogs_post_body h1,
#cnblogs_post_body h2,
#cnblogs_post_body h3,
#cnblogs_post_body h4    {
    background: #037cdf;
    border-radius: 6px 6px 6px 6px;
    box-shadow: 0 0 0 1px #5F5A4B, 1px 1px 6px 1px rgba(10, 10, 0, 0.5);
    color: #FFFFFF;
    font-family: "微软雅黑" , "宋体" , "黑体" ,Arial;
    font-weight: bold;
    text-shadow: 2px 2px 3px #222222;
}
#cnblogs_post_body h1 {
    font-size: 23px;
}
#cnblogs_post_body h2 {
    font-size: 20px;
}
#cnblogs_post_body h3 {
    font-size: 18px;
}
#cnblogs_post_body h1,
#cnblogs_post_body h2,
#cnblogs_post_body h3 {
    height: 25px;
    line-height: 25px;
    margin: 18px 0 !important;
    padding: 8px 0 5px 5px;
}
#cnblogs_post_body h4 {
    font-size: 16px;
    height: 24px;
    line-height: 23px;
    margin: 12px 0 !important;
    padding: 5px 0 5px 10px;
}
#cnblogs_post_body h3    {
    background: #399ab2;
    border-radius: 6px 6px 6px 6px;
    box-shadow: 0 0 0 1px #5F5A4B, 1px 1px 6px 1px rgba(10, 10, 0, 0.5);
    color: #FFFFFF;
    font-family: "微软雅黑" , "宋体" , "黑体" ,Arial;
    font-size: 18px;
    font-weight: bold;
    margin: 18px 0 !important;
    padding: 8px 0 5px 5px;
    text-shadow: 2px 2px 3px #222222;
}
#blog_post_info_block {
}
#green_channel {
    width: 100%;
}
#green_channel a {
    font-size: 25px;
}
#author_profile a {
    display: inline-block;
    color: #000;
    font-size: 17px;
    margin: 5px;
    float: left;
}
#div_digg {
}
.c_b_p_desc {
    font-size: 15px;
    color: #333;
    font-family: "华文中宋";
}
.c_b_p_desc a {
    color: rgb(0, 0, 186);
    float: right;
    text-decoration: underline !important;
    font-family: "华文楷体";
}
.c_b_p_desc a:hover {
    color: #0169e1;
}
.postDesc {
    margin-bottom: 30px;
}
.postDesc,
.postDesc a,
.postDesc span {
    font-family: "微软雅黑";
    text-decoration: none;
    color: #777777;
}

.feedback_area_title {
    font-size: 25px;
}
.feedbackItem {
    position: relative;
    padding: 15px 0 15px 60px;
    margin: 0;
    font-size: 13px
}
.feedbackItem:before {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 90px;
    display: block;
    z-index: 0;
    width: 2px;
    content: "";
    background-color: #e1e4e8
}
.feedbackAvatar {
    position: absolute;
    left: 1px
}
.feedbackAvatar img {
    width: 40px;
    height: 40px;
    border: 1px solid #d1d5da;
    padding: 2px;
    border-radius: 3px
}
.feedbackListSubtitle {
    clear: both;
    align-items: center;
    color: #586069;
    flex-direction: row-reverse;
    background-color: #f6f8fa;
    border: 1px solid #e9e9e9;
    border-bottom: 1px solid #e9e9e9;
    border-top-left-radius: 5px;
    border-top-right-radius: 5px;
    padding: 10px 20px;
    position: relative;
    white-space: nowrap;
    text-overflow: ellipsis
}
.feedbackListSubtitle a:active,
.feedbackListSubtitle a:link,
.feedbackListSubtitle a:visited {
    color: #777;
    font-weight: 700
}
.feedbackListSubtitle a:hover {
    color: #5c8ec6;
    text-decoration: underline
}
.feedbackListSubtitle b {
    color: #5c8ec6
}
.feedbackListSubtitle:before {
    position: absolute;
    top: 11px;
    right: 100%;
    left: -16px;
    display: block;
    width: 0;
    height: 0;
    pointer-events: none;
    content: " ";
    border-color: transparent;
    border-style: solid solid outset;
    border-width: 8px;
    border-right-color: #d1d5da
}
.feedbackListSubtitle:after,
.feedbackListSubtitle-louzhu:after {
    position: absolute;
    top: 11px;
    right: 100%;
    left: -16px;
    display: block;
    width: 0;
    height: 0;
    pointer-events: none;
    content: " ";
    border-color: transparent;
    border-style: solid solid outset;
    margin-top: 1px;
    margin-left: 2px;
    border-width: 7px
}
.feedbackListSubtitle:after {
    border-right-color: #f6f8fa
}
.feedbackListSubtitle-louzhu:after {
    border-right-color: #f1f8ff !important
}
.feedbackManage {
    width: 200px;
    text-align: right;
    float: right
}
.feedbackCon {
    padding: 10px 20px;
    min-height: 35px;
    line-height: 1.5;
    border: 1px solid #e9e9e9;
    border-top: 0;
    border-bottom-left-radius: 5px;
    border-bottom-right-radius: 5px;
    background: #fff;
    position: relative
}
.feedbackListSubtitle-louzhu {
    background-color: #f1f8ff !important;
    border-bottom-color: #c0d3eb !important
}
.comment_vote a {
    color: #333;
}
.comment_vote a:hover {
    color: #056add;
}

#comment_form {
}
#comment_nav {
    margin-bottom: 30px;
    border-bottom: 2px dashed #037cdf;
}
#comment_nav a:hover {
    color: #056add;
}
.commentbox_main {
    width: 100%;
}
#comment_form_container p {
    color: #777;
}
#commentbox_opt a,
#btn_comment_submit {
    display: inline-block;
    background: #0367da;
    text-decoration: none;
    color: #fff;
    margin: 10px 20px 10px 0px;
    padding: 0 10px;
    width: auto;
    height: auto;
    border: none;
    line-height: 28px;
    font-size: 14px;
    font-weight: bold;
    border-radius: 5px;
    text-transform: uppercase;
    transition: all .4s;
    -webkit-transition: all .4s;
    -moz-transition: all .4s;
    -ms-transition: all .4s;
    -o-transition: all .4s;
    position: relative;
    cursor: pointer;
}
#commentbox_opt a:hover,
#btn_comment_submit:hover {
    background: #519bf0;
}
#cnblogs_ch,
#opt_under_post,
#cnblogs_c1,
.under-post-card {
    display: none !important;
}

#footer {
    margin-top: 50px;
    text-align: center;
    color: #666;
}

样式修改主要就是用浏览器不断审查页面元素，找到元素对应的id或者class进行修改样式。
#cnblogs_ch, #opt_under_post, #cnblogs_c1, .under-post-card是博客园页面最底部的广告和推荐，顺手设成display: none给他隐藏了。

3. 侧边栏

我在改样式的时候一直想给侧边栏加一个文章的目录，但也懒得自己遍历全文去找各种标签，然后就用了SimpleMemory主题自带的目录窗口。
SimpleMemory自带的目录是先通过点击标题旁边的图标按钮显示出来，然后点击固定之后就会脱离文本流。
我采用的方法比较笨，用js模拟鼠标去点击上述两个按钮，然后把弹出的窗口设成fixed定位(其实已经是fixed了)，然后隐藏这个窗口自带的关闭按钮，并自己做个用于显示/隐藏这个窗口的按钮。
最后再用svg加了个返回顶部的按钮。
代码如下:

<script type="text/javascript">
    window.cnblogsConfig = {
        GhVersions: 'v1.3.2', // 版本
        blogUser: "longxiaoming", // 用户名
        blogAvatar: "https://images.cnblogs.com/cnblogs_com/blogs/786357/galleries/2285082/o_230310051136_image.png", // 用户头像
        blogStartDate: "2023-03-09", // 入园时间，年-月-日。入园时间查看方法：鼠标停留园龄时间上，会显示入园时间
    }
</script>

<script type="text/javascript">
    let titleButton = document.querySelector(".postTitle .cnblogs-toc-button")
    if (titleButton) {
        // 有标题，说明是文章页
        // 点击相关按钮显示目录导航(先点击标题按钮, 弹出临时弹窗,再点击弹窗中的固定按钮，并隐藏临时弹窗)
        titleButton.click()
        document.querySelector(".postTitle .cnblogs-toc-pinned-button").click()
        let winbox = document.getElementById("winbox-1")
        winbox.className = winbox.className.replace(/\bwinbox\b/, '')
        winbox.style.top = "150px"
        winbox.style.right = "60px"
        // 隐藏临时弹窗
        document.getElementById("tippy-1").style.display = "none"
        // 添加一个圆形的fixed按钮，点击显示/隐藏目录导航
        let button = document.createElement("button")
        button.className = "cnblogs-toc-button my-toc-button"
        button.title = "显示目录导航"
        button.setAttribute("aria-expanded", "true")
        document.body.appendChild(button)
        // 将按钮移动到winbox的右边
        let moveButton = () => {
            let winboxRect = winbox.getBoundingClientRect()
            let right = window.innerWidth - winboxRect.right
            if (right - 60 > 0) {
                button.style.right = right - 60 + "px"
                button.style.top = winboxRect.top + 20 + "px"
            } else {
                button.style.right = "10px"
                button.style.top = winboxRect.top - 50 + "px"
            }
        }
        moveButton()
        // 绑定事件，当winbox被移动时，也移动按钮
        let observer = new MutationObserver(function (mutations) {
            mutations.forEach(function (mutation) {
                if (mutation.attributeName === "style") {
                    if (winbox.style.display !== "none") {
                        moveButton()
                    }
                }
            })
        })
        observer.observe(winbox, {
            attributes: true
        })
        // 绑定按钮点击事件
        button.onclick = function () {
            if (button.getAttribute("aria-expanded") === "false") {
                button.setAttribute("aria-expanded", "true")
                button.title = "隐藏目录导航"
                winbox.style.display = "block"
            } else {
                button.setAttribute("aria-expanded", "false")
                button.title = "显示目录导航"
                winbox.style.display = "none"
            }
        }
        // 隐藏默认的关闭按钮
        document.querySelector("#winbox-1 .wb-close").style.display = "none"
    }
    // 回到顶部按钮
    let backToTopButton = document.createElement("button")
    backToTopButton.className = "my-toc-button"
    backToTopButton.title = "回到顶部"
    backToTopButton.style.right = "15px"
    backToTopButton.style.bottom = "15px"
    backToTopButton.innerHTML = '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" width="24" height="24"><path fill="currentColor" d="M12,3L2,12H7V20H17V12H22L12,3Z"></path></svg>'
    document.body.appendChild(backToTopButton)
    backToTopButton.onclick = function () {
        window.scrollTo({
            top: 0,
            behavior: "smooth"
        })
    }

</script>

<style>
    .my-toc-button {
        z-index: 999;
        position: fixed;
        width: 40px;
        height: 40px;
        background-color: #fff;
        border: none;
        outline: none;
        cursor: pointer;
        opacity: 0.7;
        border-radius: 50%;
    }

    .my-toc-button:hover {
        opacity: 1;
    }

    #winbox-1 {
        left: auto;
        position: fixed;
        box-shadow: 0 14px 28px rgb(0 0 0 / 25%), 0 10px 10px rgb(0 0 0 / 22%);
        transition: width .3s, height .3s, transform .3s, opacity .3s;
        transition-timing-function: cubic-bezier(.3, 1, .3, 1);
        will-change: transform, width, height, opacity;
        contain: layout size;
        text-align: left;
        touch-action: none;
        min-height: 35px;
    }
</style>

<script type="text/javascript">
    (function (window, document, undefined) {
        var hearts = [];
        window.requestAnimationFrame = (function () {
            return window.requestAnimationFrame ||
                window.webkitRequestAnimationFrame ||
                window.mozRequestAnimationFrame ||
                window.oRequestAnimationFrame ||
                window.msRequestAnimationFrame ||
                function (callback) {
                    setTimeout(callback, 1000 / 60);
                }
        })();
        init();
        function init() {
            css(".heart{width: 10px;height: 10px;position: fixed;background: #f00;transform: rotate(45deg);-webkit-transform: rotate(45deg);-moz-transform: rotate(45deg);}.heart:after,.heart:before{content: '';width: inherit;height: inherit;background: inherit;border-radius: 50%;-webkit-border-radius: 50%;-moz-border-radius: 50%;position: absolute;}.heart:after{top: -5px;}.heart:before{left: -5px;}");
            attachEvent();
            gameloop();
        }
        function gameloop() {
            for (var i = 0; i < hearts.length; i++) {
                if (hearts[i].alpha <= 0) {
                    document.body.removeChild(hearts[i].el);
                    hearts.splice(i, 1);
                    continue;
                }
                hearts[i].y--;
                hearts[i].scale += 0.004;
                hearts[i].alpha -= 0.013;
                hearts[i].el.style.cssText = "left:" + hearts[i].x + "px;top:" + hearts[i].y + "px;opacity:" + hearts[i].alpha + ";transform:scale(" + hearts[i].scale + "," + hearts[i].scale + ") rotate(45deg);background:" + hearts[i].color;
            }
            requestAnimationFrame(gameloop);
        }
        function attachEvent() {
            var old = typeof window.onclick === "function" && window.onclick;
            window.onclick = function (event) {
                old && old();
                createHeart(event);
            }
        }
        function createHeart(event) {
            var d = document.createElement("div");
            d.className = "heart";
            hearts.push({
                el: d,
                x: event.clientX - 5,
                y: event.clientY - 5,
                scale: 1,
                alpha: 1,
                color: randomColor()
            });
            document.body.appendChild(d);
        }
        function css(css) {
            var style = document.createElement("style");
            style.type = "text/css";
            try {
                style.appendChild(document.createTextNode(css));
            } catch (ex) {
                style.styleSheet.cssText = css;
            }
            document.getElementsByTagName('head')[0].appendChild(style);
        }
        function randomColor() {
            return "rgb(" + (~~(Math.random() * 255)) + "," + (~~(Math.random() * 255)) + "," + (~~(Math.random() * 255)) + ")";
        }
    })(window, document);
</script>

4. 样式修改后效果如下