Port admin to new layout

app/assets/stylesheets/legacy/_layout.scss

@@ -8,6 +8,13 @@ body {
   background-attachment: fixed;
 }
 
+body#admin-panel {
+  background: linear-gradient(35deg, rgba(255,0,255,0.2) 0, rgba(153,12,14,0.9) 100%),
+              url('/img/bg-1.jpg');
+  background-size: cover;
+  background-attachment: fixed;
+}
+
 .ks-site-icon {
   svg {
     display: inline-block;
@@ -60,30 +67,6 @@ body {
   }
 }
 
-body#admin-panel {
-  #wrapper {
-    > header {
-      background: $color-red-bright;
-      background: linear-gradient(35deg, rgba(255,0,255,0.2) 0, rgba(153,12,14,0.9) 100%),
-                  url('/img/bg-1.jpg');
-    }
-  }
-
-  #main-nav {
-    ul {
-      grid-template-columns: repeat(4, 1fr);
-
-      li {
-        a {
-          &.active {
-            border-bottom: 2px solid $color-red-bright;
-          }
-        }
-      }
-    }
-  }
-}
-
 .flash-msg {
   width: 100%;
   text-align: center;
@@ -123,14 +106,6 @@ main {
   table {
     width: 100%;
 
-    th, td {
-      &.hide-small {
-        @include media-max(small) {
-          display: none;
-        }
-      }
-    }
-
     th {
       color: $text-color-discreet;
       font-weight: normal;