First of all, create an album called Background in your blog (call everything for convenience)

Next, open the picture and review the elements (usually F12)?

Find http until jpg copies them (file path of picture)

Then copy the following metaphysical code

/*simplememory*/
#google_ad_c1, #google_ad_c2 {display:none;}
.syntaxhighlighter a, .syntaxhighlighter div, .syntaxhighlighter code, .syntaxhighlighter table, .syntaxhighlighter table td, 
.syntaxhighlighter table tr, .syntaxhighlighter table tbody, .syntaxhighlighter table thead, .syntaxhighlighter table caption, 
.syntaxhighlighter textarea {
font-size: 14px!important;
}
#home {
opacity: 0.80;
margin: 0 auto;
width: 85%;
min-width: 950px;
background-color: #fff;
padding: 30px;
margin-top: 30px;
margin-bottom: 50px;
box-shadow: 0 2px 6px rgba(100, 100, 100, 0.3);
}
#blogTitle h1 {
font-size: 30px;
font-weight: bold;
font-family: "Comic Sans MS";
line-height: 1.5em;
margin-top: 20px;
color: #515151;
}
#navList a:hover {
color: #4C9ED9;
text-decoration: none;
}
#navList a {
display: block;
width: 5em;
height: 22px;
float: left;
text-align: center;
padding-top: 18px;
}
#navigator {
font-size: 15px;
border-bottom: 1px solid #ededed;
border-top: 1px solid #ededed;
height: 50px;
clear: both;
margin-top: 25px;
}
.catListTitle {
margin-top: 21px;
margin-bottom: 10.5px;
text-align: left;
border-left: 10px solid rgba(82, 168, 236, 0.8);
padding: 10px 0 14px 10px;
background-color: #f5f5f5;
}
#ad_under_post_holder #google_ad_c1,#google_ad_c2{  
display: none !important;
}
body {
color: #000;
background: url(http://images2015.cnblogs.com/blog/969197/201703/969197-20170325160900815-1058599404.jpg
) fixed;
background-size: 100%;
background-repeat: no-repeat;
font-family: "Helvetica Neue",Helvetica,Verdana,Arial,sans-serif;
font-size: 12px;
min-height: 101%;
}
#topics .postTitle {
border: 0px;
font-size: 200%;
font-weight: bold;
float: left;
line-height: 1.5;
width: 100%;
padding-left: 5px;
}

div.commentform p{
margin-bottom:10px;
}
.comment_btn {
padding: 5px 10px;
height: 35px;
width: 90px;
border: 0 none;
border-radius: 5px;
background: #ddd;
color: #999;
cursor:pointer;
font-family: "Lato", Helvetica Neue, Helvetica, Microsoft Yahei, Song style, Arial, sans-serif;
text-shadow: 0 0 1px #fff;
display: inline !important;
}
.comment_btn:hover{
padding: 5px 10px;
height: 35px;
width: 90px;
border: 0 none;
border-radius: 5px;
background: #258fb8;
color: white;
cursor:pointer;
font-family: "Lato", Helvetica Neue, Helvetica, Microsoft Yahei, Song style, Arial, sans-serif;
text-shadow: 0 0 1px #fff;
display: inline !important;
}
#commentform_title {
background-image:none;
background-repeat:no-repeat;
margin-bottom:10px;
padding:0;
font-size:24px;
}
#commentbox_opt,#commentbox_opt + p {
text-align:center;
}
.commentbox_title {
width: 100%;
}
#tbCommentBody {
font-family:'Microsoft Yahei', Microsoft Yahei, Song style, sans-serif;
margin-top:10px;
max-width:100%;
min-width:100%;
background:white;
color:#333;
border:2px solid #fff;
box-shadow:inset 0 0 8px #aaa;
// padding:10px;
height:250px;
font-size:14px;
min-height:120px;
}
.feedbackItem {
font-size:14px;
line-height:24px;
margin:10px 0;
padding:20px;
background:#F2F2F2;
box-shadow:0 0 5px #aaa;
}
.feedbackListSubtitle {
font-weight:normal;
}

#blog-comments-placeholder, #comment_form {
padding: 20px;
background: #fff;
-webkit-box-shadow: 1px 2px 3px #ddd;
box-shadow: 1px 2px 3px #ddd;
margin-bottom: 50px;
}
.feedback_area_title {
margin-bottom: 15px;
font-size: 1.8em;
}
.feedbackItem {
border-bottom: 1px solid #CCC;
margin-bottom: 10px;
padding: 5px;
background: rgb(248, 248, 248);
}
.color_shine {background: rgb(226, 242, 255);}
.feedbackItem:hover {-webkit-animation-name: color_shine;-webkit-animation-duration: 2s;-webkit-animation-iteration-count: infinite;}
#comment_form .title {
font-weight: normal;
margin-bottom: 15px;
}

Paste it into Management - Settings - Page Customization CSS Code

body {
color: #000;
background: url(http://images2015.cnblogs.com/blog/969197/201703/969197-20170325160900815-1058599404.jpg
) fixed;
background-size: 100%;
background-repeat: no-repeat;
font-family: "Helvetica Neue",Helvetica,Verdana,Arial,sans-serif;
font-size: 12px;
min-height: 101%;
}

Find this paragraph, see http? Change this sentence into the path of the picture you just copied and save it.

When Dangdang ~the background is revised! White skin is recommended.