[fix] background image of THU

app/javascript/styles/thu/diff.scss

@@ -2,14 +2,14 @@
 /* Status */
 /* Drawer */
 body {
-	background: rgba(73, 58, 99, 1) url(https://www.tsinghua.edu.cn/images/footer.jpg) no-repeat fixed;
+	background: rgba(73, 58, 99, 1) url(https://www.tsinghua.edu.cn/images/nav-bg.jpg) no-repeat fixed;
 	background-size: cover;
 	background-attachment: fixed;
   background-position: center;
   height: 100vh !important;
 }
 body.theme-thu {
-	background: rgba(73, 58, 99, 1) url(https://www.tsinghua.edu.cn/images/footer.jpg) no-repeat fixed;
+	background: rgba(73, 58, 99, 1) url(https://www.tsinghua.edu.cn/image/nav-bg.jpg) no-repeat fixed;
 	background-size: cover;
 	background-attachment: fixed;
   background-position: center;