FIX: Don't lose background class while navigating from /latest to

`/new`

app/assets/javascripts/discourse/mixins/add-category-class.js.es6

@@ -0,0 +1,23 @@
+// Mix this in to a view that has a `categoryId` property to automatically
+// add it to the body as the view is entered / left / model is changed.
+// This is used for keeping the `body` style in sync for the background image.
+export default {
+  _observeOnce: function() { this.get('categoryId'); }.on('init'),
+
+  _removeClasses: function() {
+    $('body').removeClass(function(idx, css) {
+      return (css.match(/\bcategory-\d+/g) || []).join(' ');
+    });
+  },
+
+  _categoryChanged: function() {
+    var categoryId = this.get('categoryId');
+    this._removeClasses();
+
+    if (categoryId) {
+      $('body').addClass('category-' + categoryId);
+    }
+  }.observes('categoryId'),
+
+  _leaveView: function() { this._removeClasses(); }.on('willDestroyElement')
+};

app/assets/javascripts/discourse/routes/discovery_route_builders.js

@@ -103,7 +103,6 @@ function buildCategoryRoute(filter, params) {
         this.replaceWith('/404');
         return;
       }
-      this.controllerFor('application').set('styleCategory', model);
 
       var self = this,
           noSubcategories = params && !!params.no_subcategories,
@@ -167,7 +166,6 @@ function buildCategoryRoute(filter, params) {
     deactivate: function() {
       this._super();
       this.controllerFor('search').set('searchContext', null);
-      this.controllerFor('application').set('styleCategory', null);
     },
 
     actions: {

app/assets/javascripts/discourse/views/navigation-category.js.es6

@@ -0,0 +1,5 @@
+import AddCategoryClass from 'discourse/mixins/add-category-class';
+
+export default Em.View.extend(AddCategoryClass, {
+  categoryId: Em.computed.alias('controller.category.id'),
+});

app/assets/stylesheets/common/base/discourse.scss

@@ -21,9 +21,14 @@ a.no-href {
   cursor: pointer;
 }
 
+html {
+  height: 100%;
+}
+
 body {
   background-attachment: fixed;
   background-size: cover;
+  min-height: 100%;
 
   button.ok {
     background: $success;