Refactor side navigation CSS

less/lib/sideNav.less

@@ -48,8 +48,7 @@
   }
 }
 
-@media @tablet {
-  .sideNav {
+.sideNav--horizontal {
   padding: 15px 0;
   white-space: nowrap;
   overflow: auto;
@@ -66,7 +65,7 @@
 
   > ul > li, .Dropdown-menu > li {
     display: inline-block;
-      margin-right: 20px;
+    margin: 0 20px 0 0;
   }
   .Dropdown-separator {
     display: none;
@@ -84,6 +83,10 @@
     position: static;
   }
 }
+@media @tablet {
+  .sideNav {
+    .sideNav--horizontal();
+  }
 }
 
 @media @desktop-up {
@@ -97,7 +100,7 @@
       margin-top: 30px;
 
       &.affix {
-        top: 56px;
+        top: @header-height;
       }
       > li {
         margin-bottom: 10px;