Improve SASS code style.

assets/css/_addon/main.scss

@@ -106,7 +106,7 @@ $sidebar-display: "sidebar-display";
   }
 
   .sidebar-bottom {
-    .icon-border+a { // the icon behide mode-toggle
+    .icon-border + a { // the icon behide mode-toggle
       margin-left: .1rem;
     }
   }
@@ -185,7 +185,7 @@ $sidebar-display: "sidebar-display";
       margin-bottom: .5rem; // icons may have multi lines
     }
 
-    a:hover, #mode-toggle-wrapper>i:hover {
+    a:hover, #mode-toggle-wrapper > i:hover {
       color: #fff;
     }
 
@@ -211,7 +211,7 @@ $sidebar-display: "sidebar-display";
 } // #sidebar
 
 @media (hover: hover) {
-  #sidebar ul>li:last-child::after {
+  #sidebar ul > li:last-child::after {
     -webkit-transition: top .5s ease;
     -moz-transition: top .5s ease;
     -o-transition: top .5s ease;
@@ -242,7 +242,7 @@ $sidebar-display: "sidebar-display";
     transition: border-color 0.35s ease-in-out;
   }
 
-  &:hover>a {
+  &:hover > a {
     border-color: #fff;
   }
 
@@ -448,7 +448,7 @@ $sidebar-display: "sidebar-display";
   @include pl-pr(0);
 }
 
-#main>div.row:first-child>div {
+#main > div.row:first-child > div {
   &:nth-child(1), &:nth-child(2) {
     margin-top: $topbar-height; /* same as the height of topbar */
   }
@@ -544,7 +544,7 @@ footer {
 
 
 #access-tags {
-  >div.post-content>div {
+  >div.post-content > div {
     max-width: 80%;
   }
   .post-tag {
@@ -676,7 +676,7 @@ sup {
     &:not(:last-child) {
       margin-bottom: -.8rem;
     }
-    &:target>p {
+    &:target > p {
       background-color: var(--footnote-target-bg);
       width: fit-content;
       -webkit-transition: background-color 1.5s ease-in-out;
@@ -693,7 +693,7 @@ sup {
     -webkit-transition: background-color 1.5s ease-in-out; /* Safari prior 6.1 */
     transition: background-color 1.5s ease-in-out;
   }
-  @at-root sup:target>a#{&} {
+  @at-root sup:target > a#{&} {
     background-color: var(--footnote-target-bg);
     padding: 0 2px;
   }
@@ -928,7 +928,7 @@ div.post-content .table-wrapper {
 
   $footer-height: 6rem; // overwrite
 
-  #main>div.row:first-child>div:first-child {
+  #main > div.row:first-child > div:first-child {
     min-height: calc(100vh - #{$topbar-height} - #{$footer-height});
   }
 
@@ -941,7 +941,7 @@ div.post-content .table-wrapper {
     }
   }
 
-  #avatar>a {
+  #avatar > a {
     width: 5rem;
     height: 5rem;
   }
@@ -951,7 +951,7 @@ div.post-content .table-wrapper {
   }
 
   /* table text in small screens */
-  div>table, p~table {
+  div > table, p ~ table {
     width: 100%;
     table-layout: fixed;
     word-wrap: break-word;
@@ -1051,8 +1051,8 @@ div.post-content .table-wrapper {
     top: 0 !important;
   }
 
-  #main>div.row:first-child>div:nth-child(1),
-  #main>div.row:first-child>div:nth-child(2) {
+  #main > div.row:first-child > div:nth-child(1),
+  #main > div.row:first-child > div:nth-child(2) {
     margin-top: 0;
   }
 
@@ -1063,7 +1063,7 @@ div.post-content .table-wrapper {
   }
 
   #search-wrapper {
-    &.loaded~a {
+    &.loaded ~ a {
       margin-right: 1rem;
     }
     .fa-times-circle {
@@ -1095,7 +1095,7 @@ div.post-content .table-wrapper {
     padding-top: 3.4rem;
   }
 
-  .footnotes ol>li {
+  .footnotes ol > li {
     padding-top: 3.5rem;
     margin-top: -4.3rem;
     &:first-child {
@@ -1106,7 +1106,7 @@ div.post-content .table-wrapper {
 
 
 @media all and (min-width: 577px) and (max-width: 1199px) {
-  footer>.d-flex>div {
+  footer>.d-flex > div {
     width: 312px;
   }
 }
@@ -1147,7 +1147,7 @@ div.post-content .table-wrapper {
     text-align: left;
   }
 
-  footer>div.d-flex {
+  footer > div.d-flex {
     width: 92%;
   }
 
@@ -1184,7 +1184,7 @@ div.post-content .table-wrapper {
     width: calc(100% - 210px);
   }
 
-  #search-results>div {
+  #search-results > div {
     max-width: 700px;
   }
 
@@ -1222,7 +1222,7 @@ div.post-content .table-wrapper {
     padding: 0;
   }
 
-  #main>div.row {
+  #main > div.row {
     -webkit-box-pack: center!important;
     -ms-flex-pack: center!important;
     justify-content: center!important;
@@ -1234,7 +1234,7 @@ div.post-content .table-wrapper {
 
 @media all and (min-width: 1200px) {
 
-  #main>div.row>div.col-xl-8 {
+  #main > div.row > div.col-xl-8 {
     -webkit-box-flex: 0;
     -ms-flex: 0 0 75%;
     flex: 0 0 75%;
@@ -1265,7 +1265,7 @@ div.post-content .table-wrapper {
     width: calc(100% - 260px);
   }
 
-  #search-results>div {
+  #search-results > div {
     max-width: 46%;
     &:nth-child(odd) {
       margin-right: 1.5rem;
@@ -1283,7 +1283,7 @@ div.post-content .table-wrapper {
     font-size: 1.03rem;
   }
 
-  footer>div.d-felx {
+  footer > div.d-felx {
     width: 85%;
   }
 
@@ -1291,7 +1291,7 @@ div.post-content .table-wrapper {
 
 @media all and (min-width: 1400px) {
 
-  #main>div.row {
+  #main > div.row {
     padding-left: calc((100% - #{$main-content-max-width}) / 2);
     >div.col-xl-8 {
       max-width: 850px;
@@ -1323,7 +1323,7 @@ div.post-content .table-wrapper {
     padding-left: 0;
   }
 
-  #main>div.row>div.col-xl-8 {
+  #main > div.row > div.col-xl-8 {
     padding-left: 0;
     >div:first-child {
       padding-left: .55rem !important;
@@ -1400,7 +1400,7 @@ div.post-content .table-wrapper {
 
     ul {
       margin-left: 3%;
-      >li>a {
+      >li > a {
         padding-left: 2.5rem;
         -webkit-box-pack: start!important;
         -ms-flex-pack: start!important;
@@ -1457,7 +1457,7 @@ div.post-content .table-wrapper {
       }
     } // .sidebar-bottom
   } // #sidebar
-  footer>div.d-flex {
+  footer > div.d-flex {
     width: 87%;
     max-width: 1140px;
   }
@@ -1482,7 +1482,7 @@ div.post-content .table-wrapper {
     max-width: calc(#{$main-content-max-width} + 20px)
   }
 
-  #main>div.row {
+  #main > div.row {
     padding-left: calc((100% - #{$main-content-max-width} - 2%) / 2);
   }
 
@@ -1502,7 +1502,7 @@ div.post-content .table-wrapper {
 }
 
 @media (min-width: 1920px) {
-  #main>div.row {
+  #main > div.row {
     padding-left: 190px;
   }